Direct Current Injection Research Articles

Frequency-tunable perpendicular spin torque oscillator

We present an experimental study on the frequency tunability of a perpendicular spin transfer torque oscillator with a perpendicularly magnetized (Co/Pd)5 reference electrode and a Co/(Pd/Co)4 composite oscillating layer of a giant magnetoresistive stack. A current-perpendicular-to-plane magnetoresistance ratio of 2.55% is obtained for the stack. Spin transfer torque induced steady oscillation with a narrow line-width has been obtained with direct current injection. As the injected dc current level is varied from 4.5 to 8.5 mA under a small constant applied field, the oscillation frequency increases from 5 to 6.2 GHz and back to 5.8 GHz. The oscillation with the narrowest linewidth occurs at the injection current magnitude at which the highest oscillation amplitude is also obtained. Micromagnetic modeling suggests that a nanomagnet above its critical single domain size is subjected to higher order spin wave generation at large current density. The spatial inhomogenity created across the nanomagnet can account for the drop in its oscillation frequency at relatively large injection currents.

Design Approach of Dynamically Reconfigurable Single Flux Quantum Logic Gates

Novel reconfigurable superconductive single flux quantum (SFQ) logic devices, the functions of which can be dynamically reconfigured by inputting control signals, have been investigated. The characteristics of single flux quantum circuits can be easily modulated by applying currents or magnetic fields because of the high sensitivity of superconductive circuits. We investigated several design approaches for the realization of dynamically reconfigurable SFQ logic devices. We employed direct current injection to the logic gate using a non-destructive read-out flip-flop. By changing the internal state of the non-destructive read-out flip-flop, the logic function can be dynamically reconfigured. We have designed and tested a dynamically reconfigurable Josephson transmission line (JTL)/delay flip-flop (DFF) circuit. The measured dc bias margin was 72.5-107.2%. Furthermore, we have demonstrated the operation of a variable bit-length shift register, composed of the dynamically reconfigurable JTL/DFF circuits. The investigated design approach can be applied to more sophisticated dynamically reconfigurable single flux quantum logic gates.

The Effect of Direct Axis Current on the Performance of the Synthetic Loading Technique

Synthetic loading is a technique that forces the machine under test to operate at rated speed, torque, and flux without the need for the test machine to be connected to an external load. The technique has been successfully applied to permanent magnet machines but it requires an inverter voltampere (VA) rating that is 1.51 pu of the rated value due to the need for instantaneous phase currents and voltages that are higher than the rated value. In order to reduce the VA rating, it is possible to inject direct axis current. This has important consequences. It reduces the ac perturbation current thereby reducing the peak instantaneous phase current. Also, by reducing the ac perturbation current, the rotor speed variation is reduced, thereby reducing the instantaneous phase voltage requirement. Both these effects reduce the VA rating of the inverter. However, this paper demonstrates through simulation and experiment that such a scheme increases the iron losses in the machine. This is important as it alters the distribution of losses which is not a desired consequence. The effect of direct axis current on the iron loss and the machine efficiency during synthetic loading is assessed and evaluated as is the effect on the minimum dc link voltage and the inverter VA requirements used to conduct the synthetic loading technique. Simulation and experimental results are used to demonstrate the effects and validate the conclusions that while direct axis current injection reduces the inverter VA rating, it reduces the accuracy of the synthetic loading technique.

Effects of direct lateral Current Injection on the Performance, Overall Efficiency and Emission Distribution in GaN LED structures: a 2D Computational Study

ABSTRACTWe study and demonstrate the potential benefits of using a transverse junction structure in GaN LEDs by simulating and comparing the structure with conventional vertical injection structures.The direct current injection component enabled by the transverse structure significantly reduces the height of the polarization-induced potential barriers and facilitates the electron flow into the active material, improving the overall efficiency. In addition, the transverse junction structure enables a more even radiative recombination distribution from different quantum wells. We estimate the attainable optical output efficiency and also discuss the influence of the active layer design on the quantum efficiency. Based on the obtained results, shifting from the conventional 1-dimensional LED structures to genuinely 2-dimensional structures may allow new possibilities to optimize LED performance.

Application of a NMDA Receptor Conductance in Rat Midbrain Dopaminergic Neurons Using the Dynamic Clamp Technique

Neuroscientists study the function of the brain by investigating how neurons in the brain communicate. Many investigators look at changes in the electrical activity of one or more neurons in response to an experimentally-controlled input. The electrical activity of neurons can be recorded in isolated brain slices using patch clamp techniques with glass micropipettes. Traditionally, experimenters can mimic neuronal input by direct injection of current through the pipette, electrical stimulation of the other cells or remaining axonal connections in the slice, or pharmacological manipulation by receptors located on the neuronal membrane of the recorded cell.Direct current injection has the advantages of passing a predetermined current waveform with high temporal precision at the site of the recording (usually the soma). However, it does not change the resistance of the neuronal membrane as no ion channels are physically opened. Current injection usually employs rectangular pulses and thus does not model the kinetics of ion channels. Finally, current injection cannot mimic the chemical changes in the cell that occurs with the opening of ion channels.Receptors can be physically activated by electrical or pharmacological stimulation. The experimenter has good temporal precision of receptor activation with electrical stimulation of the slice. However, there is limited spatial precision of receptor activation and the exact nature of what is activated upon stimulation is unknown. This latter problem can be partially alleviated by specific pharmacological agents. Unfortunately, the time course of activation of pharmacological agents is typically slow and the spatial precision of inputs onto the recorded cell is unknown.The dynamic clamp technique allows an experimenter to change the current passed directly into the cell based on real-time feedback of the membrane potential of the cell (Robinson and Kawai 1993, Sharp et al., 1993a,b; for review, see Prinz et al. 2004). This allows an experimenter to mimic the electrical changes that occur at the site of the recording in response to activation of a receptor. Real-time changes in applied current are determined by a mathematical equation implemented in hardware.We have recently used the dynamic clamp technique to investigate the generation of bursts of action potentials by phasic activation of NMDA receptors in dopaminergic neurons of the substantia nigra pars compacta (Deister et al., 2009; Lobb et al., 2010). In this video, we demonstrate the procedures needed to apply a NMDA receptor conductance into a dopaminergic neuron.

Application of a NMDA Receptor Conductance in Rat Midbrain Dopaminergic Neurons Using the Dynamic Clamp Technique

Neuroscientists study the function of the brain by investigating how neurons in the brain communicate. Many investigators look at changes in the electrical activity of one or more neurons in response to an experimentally-controlled input. The electrical activity of neurons can be recorded in isolated brain slices using patch clamp techniques with glass micropipettes. Traditionally, experimenters can mimic neuronal input by direct injection of current through the pipette, electrical stimulation of the other cells or remaining axonal connections in the slice, or pharmacological manipulation by receptors located on the neuronal membrane of the recorded cell. Direct current injection has the advantages of passing a predetermined current waveform with high temporal precision at the site of the recording (usually the soma). However, it does not change the resistance of the neuronal membrane as no ion channels are physically opened. Current injection usually employs rectangular pulses and thus does not model the kinetics of ion channels. Finally, current injection cannot mimic the chemical changes in the cell that occurs with the opening of ion channels. Receptors can be physically activated by electrical or pharmacological stimulation. The experimenter has good temporal precision of receptor activation with electrical stimulation of the slice. However, there is limited spatial precision of receptor activation and the exact nature of what is activated upon stimulation is unknown. This latter problem can be partially alleviated by specific pharmacological agents. Unfortunately, the time course of activation of pharmacological agents is typically slow and the spatial precision of inputs onto the recorded cell is unknown. The dynamic clamp technique allows an experimenter to change the current passed directly into the cell based on real-time feedback of the membrane potential of the cell (Robinson and Kawai 1993, Sharp et al., 1993a,b; for review, see Prinz et al. 2004). This allows an experimenter to mimic the electrical changes that occur at the site of the recording in response to activation of a receptor. Real-time changes in applied current are determined by a mathematical equation implemented in hardware. We have recently used the dynamic clamp technique to investigate the generation of bursts of action potentials by phasic activation of NMDA receptors in dopaminergic neurons of the substantia nigra pars compacta (Deister et al., 2009; Lobb et al., 2010). In this video, we demonstrate the procedures needed to apply a NMDA receptor conductance into a dopaminergic neuron.

Rate maintenance and resonance in the entorhinal cortex

Throughout the brain, neurons encode information in fundamental units of spikes. Each spike represents the combined thresholding of synaptic inputs and intrinsic neuronal dynamics. Here, we address a basic question of spike train formation: how do perithreshold synaptic inputs perturb the output of a spiking neuron? We recorded from single entorhinal principal cells in vitro and drove them to spike steadily at ∼5 Hz (theta range) with direct current injection, then used a dynamic-clamp to superimpose strong excitatory conductance inputs at varying rates. Neurons spiked most reliably when the input rate matched the intrinsic neuronal firing rate. We also found a striking tendency of neurons to preserve their rates and coefficients of variation, independently of input rates. As mechanisms for this rate maintenance, we show that the efficacy of the conductance inputs varied with the relationship of input rate to neuronal firing rate, and with the arrival time of the input within the natural period. Using a novel method of spike classification, we developed a minimal Markov model that reproduced the measured statistics of the output spike trains and thus allowed us to identify and compare contributions to the rate maintenance and resonance. We suggest that the strength of rate maintenance may be used as a new categorization scheme for neuronal response and note that individual intrinsic spiking mechanisms may play a significant role in forming the rhythmic spike trains of activated neurons; in the entorhinal cortex, individual pacemakers may dominate production of the regional theta rhythm.

Synaptic transmission in the inferior mesenteric ganglion of hypertensive and normotensive rats

The inferior mesenteric ganglion (IMG) is a prevertebral sympathetic ganglion that innervates the lower abdominal and pelvic viscera. While extensive studies have been performed on the IMG of several species, there is very little information available concerning the rat IMG. Because of the importance of the mesenteric circulation in the regulation of systemic blood pressure and in the genesis of salt‐sensitive hypertension, we compared the properties and response profiles to pre‐ganglionic input of IMG neurons in normotensive (NT) and hypertensive (HT) animals using intracellular recording in vitro. All rats were uninephrectomized 4 weeks prior to experiments. HT rats received 200mg/kg of deoxycorticosterone s.q. and 1%NaCl/0.2%KCl in drinking water. NT animals (mean arterial pressure < 130mmHg) received tap water. Resting membrane potential, rheobasic current, action potential amplitude, input resistance, and membrane time constant show no significant differences between NT and HT animals. In contrast to the findings in the IMG of other species, nearly all neurons (94% in HT, 91% in NT rats) showed a phasic response to direct current injection. This is the first study of the IMG of the hypertensive rat. While there is a predominance of phasic neurons in this ganglion, changes in sympathetic outflow that occur with hypertension are not due to alterations in the basic properties of the ganglionic neurons. Supported by NIH grant HL70687

Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters

Limitation of direct current (DC) injection into the alternating current (AC) network is an important operational requirement for grid-connected photovoltaic (PV) systems. One way to ensure that this requirement is met is to use a power transformer as interface to the AC network. But this adds costs, mass, volume and power losses. In a transformerless system, the inverter forming part of the PV system has to be operated so that the DC content in its output current is below the specified limits. Ideally, there should be no DC at the output of the inverter, but in practice, in the absence of special measures, a small amount of DC current is present. A technique for elimination of the DC-offset is proposed. It is based on the sensing of the DC-offset voltage at the output of the inverter. A sensor output is used to drive a feedback system designed to control the operation of the inverter so that the DC-offset is forced to stay within the acceptable limits. A mathematical model for the DC-offset controller is derived. A design procedure, based on the model, is proposed for the controller. The results of tests performed on a system of 1 kW nominal rating provide validation for the mathematical model.

Synaptic and Network Mechanisms of Sparse and Reliable Visual Cortical Activity during Nonclassical Receptive Field Stimulation

During natural vision, the entire visual field is stimulated by images rich in spatiotemporal structure. Although many visual system studies restrict stimuli to the classical receptive field (CRF), it is known that costimulation of the CRF and the surrounding nonclassical receptive field (nCRF) increases neuronal response sparseness. The cellular and network mechanisms underlying increased response sparseness remain largely unexplored. Here we show that combined CRF + nCRF stimulation increases the sparseness, reliability, and precision of spiking and membrane potential responses in classical regular spiking (RS(C)) pyramidal neurons of cat primary visual cortex. Conversely, fast-spiking interneurons exhibit increased activity and decreased selectivity during CRF + nCRF stimulation. The increased sparseness and reliability of RS(C) neuron spiking is associated with increased inhibitory barrages and narrower visually evoked synaptic potentials. Our experimental observations were replicated with a simple computational model, suggesting that network interactions among neuronal subtypes ultimately sharpen recurrent excitation, producing specific and reliable visual responses.

Burst firing induces postsynaptic LTD at developing mossy fibre–CA3 pyramid synapses

Synaptic development is an activity-dependent process utilizing coordinated network activity to drive synaptogenesis and subsequent refinement of immature connections. Hippocampal CA3 pyramidal neurons (PYRs) exhibit intense burst firing (BF) early in development, concomitant with the period of mossy fibre (MF) development. However, whether developing MF-PYR synapses utilize PYR BF to promote MF synapse maturation remains unknown. Recently, we demonstrated that transient tonic depolarization of postsynaptic PYRs induces a persistent postsynaptic form of long-term depression (depolarization-induced long-term depression, DiLTD) at immature MF-PYR synapses. DiLTD induction is NMDAR independent but does require postsynaptic Ca(2+) influx through L-type voltage gated Ca(2+) channels (L-VGCCs), and is expressed as a reduction in AMPAR function through the loss of GluR2-lacking AMPARs present at immature MF-PYR synapses. Here we examined whether more physiologically relevant phasic L-VGCC activation by PYR action potential (AP) BF activity patterns can trigger DiLTD. Using combined electrophysiological and Ca(2+) imaging approaches we demonstrate that PYR BF effectively drives L-VGCC activation and that brief periods of repetitive PYR BF, produced by direct current injection or intrinsic network activity induces NMDAR-independent LTD by promoting Ca(2+) influx through the activated L-VGCCs. This BF induced LTD, just like DiLTD, is specific for developing MF-PYR synapses, is PICK1 dependent, and is expressed postsynaptically. Our results demonstrate that DiLTD can be induced by phasic L-VGCC activation driven by PYR BF, suggesting the engagement of natural PYR network activity patterns for MF synapse maturation.

Experimental facility and methodology for systematic studies of cold startability in direct injection Diesel engines

Cold start at low temperatures in current direct injection (DI) Diesel engines is a problem which has not yet been properly solved and it becomes particularly critical with the current trend to reduce the engine compression ratio. Although it is clear that there are some key factors whose control leads to a proper cold start process, their individual relevance and relationships are not clearly understood. Thus, efforts on optimization of the cold start process are mainly based on a trial-and-error procedure in climatic chambers at low ambient temperature, with serious limitations in terms of measurement reliability during such a transient process, low repeatability and experimental cost. This paper presents a novel approach for an experimental facility capable of simulating real engine cold start, at room temperature and under well-controlled low speed and low temperature conditions. It is based on an optical single cylinder engine adapted to reproduce in-cylinder conditions representative of those of a real engine during start at cold ambient temperatures (of the order of −20 °C). Such conditions must be realistic, controlled and repeatable in order to perform systematic studies in the borderline between ignition success and misfiring. An analysis methodology, combining optical techniques and heat release analysis of individual cycles, has been applied.

Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers

Thin film metal-oxide-semiconductor light emitting devices (LEDs) based on nanocrystalline silicon multilayer structure were grown by plasma-enhanced chemical vapor deposition. Room temperature electroluminescence was studied under direct current and time-resolved pulsed-current injection schemes. Multilayer LEDs operating at voltages below 5 V and electroluminescence turn-on voltage of 1.4–1.7 V are demonstrated. The turn-on voltage is less than 3.2 V which corresponds to the barrier height at the silicon oxide interface for electrons. Electrical injection in the multilayer LED is controlled by direct tunneling of electrons and holes among silicon nanocrystals. This injection regime is different than the Fowler–Nordheim tunneling that controls the electron injection in single thick layer LED operating at high voltages. A comparison of the power efficiency for the multilayer based LED and a similar single thick layer LED shows larger power efficiency for the former than for the second. Our results open new directions in the development of highly efficient room temperature silicon based LED.

Membrane Resonance in Bursting Pacemaker Neurons of an Oscillatory Network Is Correlated with Network Frequency

Network oscillations typically span a limited range of frequency. In pacemaker-driven networks, including many central pattern generators (CPGs), this frequency range is determined by the properties of bursting pacemaker neurons and their synaptic connections; thus, factors that affect the burst frequency of pacemaker neurons should play a role in determining the network frequency. We examine the role of membrane resonance of pacemaker neurons on the network frequency in the crab pyloric CPG. The pyloric oscillations (frequency of approximately 1 Hz) are generated by a group of pacemaker neurons: the anterior burster (AB) and the pyloric dilator (PD). We examine the impedance profiles of the AB and PD neurons in response to sinusoidal current injections with varying frequency and find that both neuron types exhibit membrane resonance, i.e., demonstrate maximal impedance at a given preferred frequency. The membrane resonance frequencies of the AB and PD neurons fall within the range of the pyloric network oscillation frequency. Experiments with pharmacological blockers and computational modeling show that both calcium currents I(Ca) and the hyperpolarization-activated inward current I(h) are important in producing the membrane resonance in these neurons. We then demonstrate that both the membrane resonance frequency of the PD neuron and its suprathreshold bursting frequency can be shifted in the same direction by either direct current injection or by using the dynamic-clamp technique to inject artificial conductances for I(h) or I(Ca). Together, these results suggest that membrane resonance of pacemaker neurons can be strongly correlated with the CPG oscillation frequency.

Anesthetics Discriminate Between Tonic and Phasic γ-Aminobutyric Acid Receptors on Hippocampal CA1 Neurons

Anesthesia is produced by a depression of neuronal signaling in the central nervous system (CNS); however, the mechanism(s) of action underlying this depression remain unclear. Recent studies have indicated that anesthetics can enhance inhibition of CNS neurons by increasing current flow through tonic gamma-aminobutyric acid (GABA(A)) receptor gated chloride channels in their membranes. Enhanced tonic inhibition would contribute to CNS depression produced by anesthetics, but it remains to be determined to what extent anesthetic actions at these receptors contribute to CNS depression. In the present study, we compared and contrasted the involvement of tonic versus synaptic GABA(A) receptors in the functional depression of CNS neurons produced by isoflurane and thiopental. In rat hippocampal slices, whole cell patch clamp recordings were used to study anesthetic effects on CA1 neuron intrinsic excitability, and population spike recordings were used to investigate effects on synaptically evoked discharge. These responses were chosen to test whether anesthetic effects on GABA receptors alter single neuron discharge and/or circuit level synaptic functioning. Phasic (synaptic) GABA receptors were selectively blocked using the GABA(A) antagonist gabazine and tonic responses were blocked using the chloride channel blocker picrotoxin. Clinically relevant and equi-effective concentrations of thiopental and isoflurane depressed CA1 neuron synaptically evoked discharge. This depression was partially reversed by blocking synaptic GABA(A) receptors with gabazine (20 microM). The thiopental-induced depression was reversed by approximately 60%, but the isoflurane-induced depression was reversed by only approximately 20%. Blocking tonic GABA(A) receptors with the addition of 100 microM picrotoxin produced an additional 40% reversal of the thiopental-induced depression, but no additional reversal was seen for isoflurane-depressed responses. In response to direct DC current injection, CA1 neuron discharge was depressed by thiopental and membrane conductance was increased. Both of these effects were reversed by picrotoxin, but not by gabazine. Isoflurane, in contrast, neither depressed current-evoked discharge, nor altered the membrane conductance of CA1 neurons. These results indicate that general anesthetics discriminate between synaptic and tonic GABA(A) receptors. Effects on both phasic and tonic receptors combined to depress circuit responses produced by thiopental, whereas only effects on synaptic GABA receptors appeared to play an important role for isoflurane. Together with the other known sites of action for these two anesthetics, our results support a multisite, agent-specific mechanism for anesthetic actions.

Electrical excitability of early neurons in the human cerebral cortex during the second trimester of gestation.

Information about development of the human cerebral cortex (proliferation, migration, and differentiation of neurons) is largely based on postmortem histology. Physiological properties of developing human cortical neurons are difficult to access experimentally and therefore remain largely unexplored. Animal studies have shown that information about the arousal of electrical activity in individual cells within fundamental cortical zones (subventricular zone [SVZ], intermediate zone, subplate [SP], and cortical plate [CP]) is necessary for understanding normal brain development. Here we ask where, in what cortical zone, and when, in what gestational week (gw), human neurons acquire the ability to generate nerve impulses (action potentials [APs]). We performed electrical recordings from individual cells in acute brain slices harvested postmortem from the human fetal cerebral cortex (16-22 gw). Tetrodotoxin-sensitive Na(+) current occurs more frequently among CP cells and with significantly greater peak amplitudes than in SVZ. As early as 16 gw, a relatively small population of CP neurons (27%) was able to generate sodium APs upon direct current injection. Neurons located in the SP exhibited the highest level of cellular differentiation, as judged by their ability to fire repetitive APs. At 19 gw, a fraction of human CP and SP neurons possess beta IV spectrin-positive axon initial segments populated with voltage-gated sodium channels (PanNav). These results yield the first physiological characterization of developing human fetal cortical neurons with preserved morphologies in intact surrounding brain tissue.

T-type calcium channels mediate rebound firing in intact deep cerebellar neurons

Neurons of the deep cerebellar nuclei (DCN) form the main output of the cerebellar circuitry and thus play an important role in cerebellar motor coordination. A prominent biophysical property observed in rat DCN neurons is rebound firing; a brief but strong hyperpolarizing input transiently increases their firing rate to much higher levels compared with that prior to the inhibitory input. Low-threshold T-type voltage-gated calcium channels have been suspected for a long time to be responsible for this phenomenon, but direct pharmacological evidence in support of this proposition is lacking. Even though a multitude of functional roles has been assigned to rebound firing in DCN neurons, their prevalence under physiological conditions is in question. Studies aimed at delineating the physiological role of rebound firing are hampered by the lack of a good pharmacological blocker. Here we show that mibefradil, a compound that blocks T-type calcium channels, potently blocks rebound firing in DCN neurons. In whole-cell experiments both mibefradil and NNC 55-0396 [(1S,2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride]. a more selective T-type calcium channel blocker, effectively blocked rebound firing produced by direct current injection. Thus, mibefradil and other T-type channel modulators may prove to be invaluable tools for elucidating the functional importance of DCN rebound firing in cerebellar computation.

Design and experimental verification of a readout integrated circuit for uncooled focal plane arrays

A complementary metal oxide semiconductor (CMOS) readout integrated circuit (ROIC) for an uncooled focal plane array (UFPA) is presented. The circuit consists of four major parts: a bolometer current direct injection (BCDI) input circuit, a column-shared capacitor feedback transimpedance amplifier (CTIA) integration circuit, a column-shared correlated double sampling (CDS) circuit, and a common output circuit. By applying the BCDI input circuit and the column-shared integration circuit of CTIA structure, high performance (high gain, a highly stable detector bias, and high photon current injection efficiency) is realized with a small pixel size. Moreover, the CDS circuit is utilized to reduce or eliminate noise of the readout circuit, and the common output circuit is utilized to improve the speed performance of the ROIC under low power dissipation. An experimental readout chip for a 45-µm-pitch 64×64 element VO2-based UFPA has been designed and fabricated. The measurement results of the fabricated readout chip at 298 K with 5-V supply voltage have successfully verified the readout function and the performance improvement. The proposed CMOS ROIC can be applied to a micro bolometric UFPA.

Correlation of Direct Current Injection (DCI) and Free-Field Illumination for HIRF Certification

The direct current injection (DCI) method, sometimes also referred to as direct drive, for aircraft high-intensity radiated field (HIRF) certification is evaluated. The method aims at reducing the necessity of resource-intensive radiated field testing at frequencies below the very high frequency band. Surface currents of a fuselage model are evaluated both analytically for incident fields and using DCI techniques. Resulting conductor currents occurring inside the fuselage model are measured and compared for both the incident field and DCI measurement techniques. The comparison approach is a direct one, meaning that no transfer function is applied between the methods.

Continuous-Wave Operation of GaN Based Multi-Quantum-Well Laser Diode at Room Temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5μm × 800μm ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110 mA and 10.5 V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12° and 32°, respectively.