Pulsed Current-voltage Characteristics Research Articles

Improved power and temperature performance of half-disk diode microlasers.

The power and temperature characteristics of Ø200 µm half-disk microlasers with a half-ring metal contact and high-density InGaAs/GaAs quantum dots are studied. In a continuous wave (CW) mode, the maximal optical power at 20°C was 134 mW, and the maximal CW lasing temperature reached 113°C. In a pulsed regime the maximal optical power of 1.6 W, limited by catastrophic degradation, was achieved. By comparing the CW and pulsed current-voltage characteristics, the dependence of a microlaser temperature on CW pumping current was determined. At CW currents corresponding to the maximal wall-plug efficiency, the maximal optical power, and complete lasing quenching, the laser temperatures were 60, 99, and 149°C, respectively.

Space-charge domains in n-type GaN epilayers under pulsed electric field

Formation and drift of space-charge domains with velocity of sound were experimentally observed in charge current traces of a high-quality lightly doped GaN semiconductor under pulsed electric fields at room and liquid nitrogen temperatures. A GaN epilayer was developed on an Ammono GaN substrate to achieve the electron density and low-field mobility values of 1.06 × 1016 cm−3 and 1021 cm2/V s (at 300 K) and 0.21 × 1016 cm−3 and 2652 cm2/V s (at 77 K), respectively. The formation of moving space-charge domains was observed only in samples with the lengths of 1 mm and longer arising at the critical electric fields starting from ∼0.4 and ∼0.8 kV/cm at 77 and 300 K, respectively. Basic electron transport parameters were found investigating short samples with the lengths of 65 μm and shorter in a wide range of electric fields up to 150 kV/cm, at which the thermal material breakdown occurred. The critical length of a sample for space-charge domain formation was estimated considering the acoustoelectric effects in analysis of pulsed current–voltage characteristics, thus defining the constraints for the design of GaN-based power electronic devices.

Compact Modeling of Static and Transient Effects of Buffer Traps in GaN HEMTs

We propose a physics-based analytical model that accurately captures the effects of buffer traps on dc characteristics of gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The model is then semi-analytically extended to additionally include the transient behavior. Analytical formulations for the shift in the threshold voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${(}{V}_{\text {OFF}}{)}$ </tex-math></inline-formula> and two-dimensional electron gas (2-DEG) density due to the presence of buffer traps in the steady state are presented. In pulsed operation, technology computer-aided design (TCAD) simulations indicate that a time-dependent negative potential (NP) is developed under the gate, resulting in a modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {OFF}}$ </tex-math></inline-formula> and current collapse (CC). An expression for the modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {off}}$ </tex-math></inline-formula> helps capture the pulsed current–voltage characteristics. The model captures the dependence of bias, time, temperature, trap concentration, capture cross section area, and activation energy of traps on the steady-state and transient characteristics. The model is implemented in Verilog-A in an existing compact model framework using a diode and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> sub-circuit and validated using measured data and TCAD simulations. The modeling results are in excellent agreement with the experimental data and TCAD simulations. Since the model is physics-based, it requires fewer number of parameters compared to that in the existing models.

High-voltage carrier transport measurements in graphene and MoS2

Pulsed current–voltage characteristics have been measured for CVD monolayer graphene and exfoliated MoS2 on HfO2 and Al2O3 (sapphire) under controlled lattice temperature conditions. The unintentional donor density in MoS2 is 3.6 × 1011cm−3 and hole density in graphene is 1.4 × 1012 cm−3. Graphene samples withstand 47 V bias when 10 ns electric pulses are applied and 131 V when 3 ns pulses are used. MoS2 samples suffer from thermal breakdown at 22 V on sapphire and 145 V on HfO2 upon application of 10 ns and 3 ns duration electrical pulses, respectively. The results are treated in terms of electron drift velocity estimated from the data on current and constant carrier density under the assumption of uniform electric field. The highest hole velocity of ∼1.8(3.1)×107 cm/s is estimated in graphene on sapphire(HfO2).

Self-heating controlled current–voltage and noise characteristics in graphene

Pulsed current–voltage characteristics have been measured for epitaxial SiC graphene under controlled lattice temperature conditions. The monolayer and AB stacked bilayer graphene is dry transferred on SiO2. The measured characteristics of two-terminal samples with coplanar electrodes demonstrate non-ohmic behaviour up to intermediate-high fields. At high currents thermal effects come into play and soft damage of the samples takes place. Bilayer graphene samples withstand 20 kV cm−1 electric field when few nanosecond voltages pulses are applied. The results are treated in terms of hole drift velocity estimated from the data on current under the assumption of uniform electric field and constant hole density. The highest velocity of ∼3.5–5 × 106 cm s−1 (∼1.5 × 107 cm s−1) is estimated for the bilayer (monolayer) graphene. The velocity results are interpreted with hot phonons. High frequency noise is measured at 10 GHz for the monolayer graphene and the associated shot noise is resolved.

The Impact of Interfacial Charge Trapping on the Reproducibility of Measurements of Silicon Carbide MOSFET Device Parameters

Silicon carbide is an emerging material in the field of wide band gap semiconductor devices. Due to its high critical breakdown field and high thermal conductance, silicon carbide MOSFET devices are predestined for high-power applications. The concentration of defects with short capture and emission time constants is higher than in silicon technologies by orders of magnitude which introduces threshold voltage dynamics in the volt regime even on very short time scales. Measurements are heavily affected by timing of readouts and the applied gate voltage before and during the measurement. As a consequence, device parameter determination is not as reproducible as in the case of silicon technologies. Consequent challenges for engineers and researchers to measure device parameters have to be evaluated. In this study, we show how the threshold voltage of planar and trench silicon carbide MOSFET devices of several manufacturers react on short gate pulses of different lengths and voltages and how they influence the outcome of application-relevant pulsed current-voltage characteristics. Measurements are performed via a feedback loop allowing in-situ tracking of the threshold voltage with a measurement delay time of only 1 μs. Device preconditioning, recently suggested to enable reproducible BTI measurements, is investigated in the context of device parameter determination by varying the voltage and the length of the preconditioning pulse.

Defect States Determining Dynamic Trapping-Detrapping in β-Ga2O3 Field-Effect Transistors

β-Ga2O3 is an intriguing material as a channel layer for the next generation high power transistors. To assess the device level effects of the traps in β-Ga2O3, the dynamic dispersion characteristics of a back-gated nanobelt β-Ga2O3 field-effect transistor prepared by mechanical exfoliation from a bulk β-Ga2O3 single crystal was investigated by the dependence of threshold voltage hysteresis on transistor transfer characteristics on the gate voltage ramp, pulsed current-voltage characteristics, and current deep level transient spectroscopy measurements. Current lag in the off-state was related to the presence of electron traps at Ec-0.75 eV, which are also present in bulk crystals and ascribed to Fe impurities or native defects. In the on-state, drain current lag was caused by surface traps with levels at Ec-(0.95–1.1) eV. Optimized passivation layers for β-Ga2O3 are required to prevent the current collapse because the device performances are affected by the environmental molecules adsorbed on the surface. Our work can pave a way to mitigating the defect-related current collapse in β-Ga2O3 electronic devices.

Trapping Phenomena in InAlN/GaN High Electron Mobility Transistors

Electron trapping-detrapping phenomena were studied for InAlN/GaN high electron mobility transistors (HEMTs) by drain current-drain voltage static and pulsed current voltage (I-V) characteristics, gate current I-Vs, transfer characteristic measurements, current deep level transient spectroscopy (CDLTS) with gate voltage pulsing, and by drain current transient measurements following both drain and gate voltage steps. The electron trapping processes are temperature activated with activation energies of 1.1 eV for drain voltage steps and 1 eV and 0.75 eV for gate voltage steps. Detrapping processes show activation energies 0.9 eV and (0.7–0.75) eV. Drain current transients are accurately described by the sum of two stretched exponents. The amplitudes of CDLTS peaks corresponding to electron trapping and electron detrapping processes show la ogarithmic dependence on the width of the injection pulse, indicating that the traps are related to dislocations.

On the radiation resistance of planar Gunn diodes with δ-doped layers

The radiation resistance of planar Gunn diodes is investigated. Based on the results of measurements of the pulsed current–voltage characteristics and computer simulations it is shown that the use of δ layers of doping impurities contributes to the higher radiation resistance of planar diodes by an order of magnitude compared to conventional Gunn diodes. The results of this study make it possible to formulate methodical guidelines to reduce the amount of computational and experimental studies without a considerable decrease in their informativity.

Design, fabrication, and analysis of p-channel arsenide/antimonide hetero-junction tunnel transistors

In this paper, we demonstrate InAs/GaSb hetero-junction (hetJ) and GaSb homo-junction (homJ) p-channel tunneling field effect transistors (pTFET) employing a low temperature atomic layer deposited high-κ gate dielectric. HetJ pTFET exhibited drive current of 35 μA/μm in comparison to homJ pTFET, which exhibited drive current of 0.3 μA/μm at VDS = −0.5 V under DC biasing conditions. Additionally, with pulsing of 1 μs gate voltage, hetJ pTFET exhibited enhanced drive current of 85 μA/μm at VDS = −0.5 V, which is the highest reported in the category of III-V pTFET. Detailed device characterization was performed through analysis of the capacitance-voltage characteristics, pulsed current-voltage characteristics, and x-ray diffraction studies.

AlGaN-GaN Metal-Insulator-Semiconductor High-Electron-Mobility Transistors With Very High- $k$ Oxynitride $\hbox{TaO}_{x} \hbox{N}_{y}$ Gate Dielectric

We investigated AlGaN-GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with high-permittivity (high-k) oxynitride TaOxNy gate dielectric (k ~24) obtained by sputtering deposition. The MIS-HEMTs show excellent pulsed current-voltage characteristics, small off-leakage currents ( 1010), and favorable threshold voltage stabilities. From comparisons with MIS-HEMTs with TaOx gate dielectric, we conclude that N incorporation in gate dielectric can suppress current collapse and deep-level states.

Edge‐field effects on gate capacitance, threshold voltage and low‐field mobility in AlGaN/GaN HEMTs

AbstractA methodologybased on output conductance model and pulsed current–voltage characteristics is presented for device parameter extraction in AlGaN/GaN HEMTs. A quiescent bias of (VDSQ, VGS Q) = (0 V, 0 V) and 0.2 µs pule width with 2 ms separation are applied to ensure that all the pulsed measurementsare performed under trap‐free operation condition.The results show that HEMTs with a shorter gate length exhibit a more negative threshold voltage, a lower low‐field mobility, and a higher capacitance than the theoretical AlGaN barrier capacitance. This is because edge field effect becomes significant in a shorter gate together with a higher lateral field effect. By comparing the measured and theoretical capacitances of AlGaN barrier, effective gate lengths are also estimated for HEMTs with different gate lengths. It is suggested that our method including the edge‐field effect is an effective way for evaluating newly‐introduced growth/processing technologies and monitoring device processing (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Fin- and Island-Isolated AlGaN/GaN HFETs

The effects of the variation of the size of isolation mesa of AlGaN/GaN heterojunction field-effect transistors (HFETs) on the device characteristics are presented for the first time. Studies on the direct current and pulsed drain and gate current-voltage characteristics demonstrate a correlation between the pinchoff voltage and the size of the isolation mesa. In this paper, devices fabricated on narrow mesas (i.e., 16 × 40 μm2 fins) and also a device fabricated on an array of very small size mesas (i.e., 16 × 7 μm2 islands) are compared with AlGaN/GaN HFETs of traditionally sized mesas (i.e., 70 × 100 μm2). All these devices show maximum extrinsic gate transconductance greater than 220 mS/mm, whereas the pinchoff voltage is observed to become less negative by reducing the size of the individual mesas. The island-isolated HFETs also enjoy a relatively higher gate transconductance.

Measurement of Pulsed Current-Voltage Characteristics of AlGaN/GaN HEMTs from Room Temperature to 15 K

We report measurements of the pulsed and dc current-voltage characteristics of AlGaN/GaN high-electron-mobility transistors as functions of geometry, temperature (from 300 down to 15 K), and operating conditions. An increase in the drain current with shortening of the pulse width from 1 µs to 400 ns is found to be significant at room temperature whilst this behavior is inverted or even removed at 77 and 15 K temperatures.

Current-controlled negative differential resistance effect induced by Gunn-type instability in n-type GaN epilayers

High-field carrier transport properties probed by pulsed current-voltage characteristics in n-type GaN epilayers have been investigated at room temperature. The threshold electric field of the Gunn effect is experimentally determined to be about 400 kV/cm with an electron peak velocity of about 1.9×107 cm/s. The current-controlled negative differential resistance effect induced by the Gunn-type instability in n-type GaN is observed, which takes the early electric breakdown of the GaN epilayers in charge.

SIMULATION AND EXPERIMENTAL RESULTS ON GaN BASED ULTRA-SHORT PLANAR NEGATIVE DIFFERENTIAL CONDUCTIVITY DIODES FOR THz POWER GENERATION

A GaN based negative differential conductivity diode utilizing transient ballistic transport effects is proposed and large-signal circuit simulations along with preliminary experimental results are presented. The diode is an n +- n - n + structure and transport is described by an empirical velocity-field relation which is derived directly from femtosecond pulse-probe measurements available in literature and incorporated into the simulations through curve fitting. Efficient THz generation is predicted as a result of ~2.8 peak-to-valley ratio. Pulsed current-voltage characteristics were measured and N -type dependence was observed.

Influence of the Structural and Compositional Properties of PECVD Silicon Nitride as a Passivation Layer for AlGaN HEMTs

We have investigated the influence of the structural and compositional properties of silicon nitride layers on the passivation of AlGaN/GaN HEMTs grown on sapphire substrates by assessing their continuous wave (CW) and pulsed current-voltage (I-V) characteristics. We have looked at the effect of various PECVD parameters like gas composition (SiH4/NH3 ratio and ammonia-free SiNx), process pressure, plasma power and deposition temperature. The best SiNx layer is Si-rich and has a refractive index of 2.01, an extinction coefficient of 0.03 at 3.44 eV and an optical band gap of 2.87eV. The best device performance was only achieved when the optimized SiNx layer was used in conjunction with a low-power Ar-plasma after the metallization of the ohmic contacts and cleaning using an ammonia dip just before the Schottky gate metallization. The latter treatment accounted for a substantial reduction of the gate and drain leakage currents densities from 6.7 mA/mm to 400 μA/mm.

Low-&amp;lt;tex&amp;gt;$kappa$&amp;lt;/tex&amp;gt;BCB Passivation on AlGaN–GaN HEMT Fabrication

Due to the stress-induced polarization effect on the GaN HEMTs, the surface passivation of the device is critical and is deserved to conduct a detailed study. It has been proven that the GaN HEMTs demonstrate nondispersive pulsed current-voltage (I-V) characteristics and better microwave power performances after passivating the Si/sub 3/N/sub 4/ film on the GaN surface. In this letter, we proposed to use the BCB material, a negative photoresist with a low-/spl kappa/ characteristic, as the surface passivation layer on GaN HEMTs fabrication. After comparing the dc I-V, pulsed I-V, RF small-signal, microwave power characteristics, and device reliability, this BCB-passivated GaN HEMT achieved better performance than the Si/sub 3/N/sub 4/ passivated device.

Current-induced effects in [formula omitted][formula omitted] single crystals

DC electrical current-dependent resistance and pulsed current–voltage characteristics as a function of temperature of mixed valent Mn oxide-based La 5 / 8 - y Pr y Ca 0.375 MnO 3 ( y = 0.35 ) single crystals are reported. We find that the low-temperature regime of this material is strongly current dependent. For small current densities ( ∼ 10 μ A / cm 2 ) , the metal–insulator transition related to the low-temperature enlargement of the ferromagnetic fraction is not observed down to 10 K. Higher current densities causes a large decrease of the resistance, which is temperature dependent and exhibits memory effects. Our results are interpreted within a scenario of strong competition between charge and ferromagnetic ordering.

60Co gamma radiation effects on DC, RF, and pulsed I– V characteristics of AlGaN/GaN HEMTs

Total-dose gamma radiation effects on static, high-frequency, and pulsed current–voltage characteristics of silicon nitride passivated AlGaN/GaN HEMTs were investigated. Passivated AlGaN/GaN HEMTs were exposed to a maximum total dose of 600 Mrad using a 60Co source under nitrogen ambient. The magnitude of the changes in the DC characteristics exhibited a monotonic increase with increasing radiation dose. At 600 Mrad dose, −0.1 V shift in threshold voltage and 3% increase in maximum transconductance was observed. High-frequency small-signal characteristics did not exhibit a significant change. Pulsed current levels increased in relation to the shift in threshold voltage, indicating no radiation damage related degradation in large signal transient behavior. The mobility, sheet carrier density, contact resistance, and sheet resistance of the sample did not exhibit measurable changes. The limited response of the devices to the high radiation dose indicates that the AlGaN/GaN HEMTs can have very high radiation hardness. The observed effects are consistent with radiation-induced trap creation.