Nonuniform Distribution Of Holes Research Articles

A study on thermal performance of a novel glazed transpired solar collector with perforating corrugated plate

Glazed transpired collectors are less efficient in collecting heat due to optical shielding, while unglazed transpired collectors experience large heat losses in areas with high crosswinds. In order to overcome these problems, a novel glazed transpired collector system with non-uniform perforation is proposed in this paper. The system consists of suction and supply ventilation installed beneath the structure and a black perforated corrugated plate. An experimental collector system was built in a laboratory to study its thermal characteristics. The influence of key parameters on the thermal efficiency of the collector was analyzed and the appropriate structural parameters were determined. In addition, the temperature rise, heat exchange efficiency, heat collection efficiency, application efficiency, and collector heat loss coefficient were determined in different conditions. The results showed that the collector provided approximately 6 °C higher temperature rise than a traditional collector, and the heat collection efficiency and heat exchange efficiency were nearly 20% larger compared to a traditional collector. The non-uniform distribution of holes in this ventilation mode can provide greater heat collection efficiency. The heat collection efficiency increased by 0.8%/°C as the inlet temperature decreased. This ventilation system provides greater heat exchange efficiency by increasing secondary heat transfer.

Tearing and related field distortions in deep-depletion charge-coupled devices

Tearing patterns affecting flat field frames in CCDs are a visually striking obstacle to performing Pixel Response Non-Uniformity corrections. These patterns can be explained by lateral field distortions, caused by the non-uniform distribution of holes in the channel stops between sensor columns. Over the course of LSST camera development, a number of practical fixes have been suggested to get rid of tearing. But applying these fixes to our 16-channel Teledyne-e2v sensors leaves at best a distortion pattern at the vertical edges of every segment. Our working hypothesis is that the origin of the tearing is the parallel clocking itself, which moves the holes that are present in the channel stops regions. The efficiency of these transfers depends strongly on the details of the clocking operations, resulting in the observed variety of distortion patterns. Removal of most of the distortion patterns can therefore be achieved by executing a purge operation, which flattens back the hole distribution in the channel stops, immediately before acquiring a frame. A more effective solution is to switch all clocking operations to use a bipolar voltage set.

A numerical study on the flow performance inside the straight pipe with perforated plates

A conventional car silencer is incorporated with several plates containing perforations for the deduction of sound waves from a car exhaust gases. Perforations in tubes or plates facilitate in developing a large variety of comprehensive models for sound attenuation. Exhaust gases passing through unimpeded straight perforated pipe forces the sound waves to dissipate the energy, thereby optimizing the performance and minimizing the back pressure exerted on the engine. On the other hand, the poorly designed perforation can deteriorate the engine performance by increasing the flow back pressure. Owing to the fact, in this work, the numerical model is based on the installation of the perforated plate with distinguishable hole sizes in a uniform circular pipe oriented normally to the mean gas flow direction. The essential function of the perforated plate is to route the gas flow in a non-uniform distribution of holes with various diameters and consequently, establishing the fully developed flow regime inside the pipe. The comprehensive description of flow performance according to the various perforated plate shapes are presented and compared to situations with no perforated plate. This work aims in demonstrating the importance of perforated plate by numerically investigating three different models, namely flat, convex and concave framed plates accomplished with pressure drop. Further, the study shows various flow characteristics associated with the velocity and turbulent intensity profiles as well as the flow uniformity depending on the perforated plates adopted. These results offer a practical guide to the best design of pipe with perforated plates.

Hole concentration dependence of the Curie temperature of (Ga,Mn)Sb in a field-effect structure

We investigate magnetotransport properties of thin (Ga,Mn)Sb layers in a field-effect structure. By changing the hole concentration p in the channel by applied electric fields, we establish the relationship between the Curie temperature TC and p, which shows γ of 1.3–1.6 in TC ∝ pγ. The exponent γ is several times larger than γ ∼ 0.2 reported previously for (Ga,Mn)As. Analyses based on the p-d Zener model taking into account of non-uniform hole distribution in the channel shows that the lager γ is explained by the presence of hole accumulation at the interface of (Ga,Mn)Sb and the gate insulator.

Thickness dependent magnetic properties of (Ga,Mn)As ultrathin films

We report on a monotonic reduction of Curie temperature in dilute ferromagnetic semiconductor (Ga,Mn)As upon a well controlled chemical-etching/oxidizing thinning from 15 nm down to complete removal of the ferromagnetic response. The effect already starts at the very beginning of the thinning process and is accompanied by the spin reorientation transition of the in-plane uniaxial anisotropy. We postulate that a negative gradient along the growth direction of self-compensating defects (Mn interstitial) and the presence of surface donor traps gives quantitative account on these effects within the p–d mean field Zener model with adequate modifications to take a nonuniform distribution of holes and Mn cations into account.

Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes

We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm2, the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs.

Temperature-Dependent Electroluminescence Efficiency in Blue InGaN–GaN Light-Emitting Diodes With Different Well Widths

Temperature dependence of electroluminescence (EL) efficiency in blue InGaN-GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with different well widths is systematically investigated. The EL efficiency at 300 K shows a maximum at the input current of 4, 10, and 60 mA for the LEDs with 1.5-, 2.0-, and 2.5-nm QWs, respectively. Nevertheless, the droop behavior at 80 K is mainly dominated by the low hole mobility and near independence on the QW thickness. According to the simulation results, it is found that the distinct efficiency droop behavior for the LEDs with different well widths at high and low temperature is strongly dependent on the effects of electron overflow and nonuniform hole distribution within the MQW region.

Curie temperature versus hole concentration in field-effect structures ofGa1−xMnxAs

The Curie temperature TC is investigated as a function of the hole concentration p in thin films of ferromagnetic semiconductor (Ga,Mn)As. The magnetic properties are probed by transport measurements and p is varied by the application of an external electric field in a field-effect transistor configuration. It is found that TC is proportional to p^{\gamma}, where the exponent \gamma = 0.19 \pm 0.02 over a wide range of Mn compositions and channel thicknesses. The magnitude of gamma is reproduced by a p-d Zener model taking into account nonuniform hole distribution along the growth direction, determined by interface states and the applied gate electric fields.

Theoretical investigation of Auger recombination on internal quantum efficiency of blue light-emitting diodes

The Auger recombination is recently proposed as one of the possible origins for the deteriorated internal quantum efficiency of InGaN light-emitting diodes. The Auger recombination behavior is quite different under widely varied Auger coefficients. The effect of Auger coefficient on the efficiency and output power is investigated numerically. The simulation results indicate that the Auger recombination with large Auger coefficient greatly decreases the efficiency in the whole current range under study. It is found that the electron current leakage and nonuniform hole distribution are the possible mechanisms responsible for the efficiency droop at high injection current.

Numerical study on strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers

The physical and optical properties of compressively strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers are numerically studied. The simulation results show that the maximum optical gain, transparency carrier densities, transparency radiative current densities, and differential gain of InGaAsP quantum wells can be efficiently improved by employing a compressive strain of approximately 1.24% in the InGaAsP quantum wells. The simulation results suggest that the 850-nm InGaAsP/InGaP vertical-cavity surface-emitting lasers have the best laser performance when the number of quantum wells is one, which is mainly attributed to the non-uniform hole distribution in multiple quantum wells due to high valence band offset.

Measurements of Electroluminescence Intensity Distribution in the Direction of Gate Width of n+ Self-Aligned Gate GaAs Metal-Semiconductor Field-Effect Transistors

We studied electroluminescence (EL) intensity distributions in the direction of gate width of n+ self-aligned gate GaAs metal-semiconductor field-effect transistors (MESFETs). Nonuniform EL was observed along the gate-width direction, suggesting the nonuniform high-field formation in the direction of the gate. It has also been found that the EL at the source side shows gentler distribution than that at the drain side. These features suggest that the nonuniform hole distribution generated by impact ionization at the drain side becomes gradual during the process of their flow into the source and gate electrodes.

Threshold current, differential gain, and relaxation resonance frequency of 1.55-μm bulk and MQW DFB laser diodes

We investigate threshold currents, differential gains, and relaxation resonance frequencies of 1.55-/spl mu/m bulk and nine-well multiple-quantum-well (MQW) distributed feedback (DFB) laser diodes (LDs) experimentally and theoretically. The experimentally obtained threshold current (I/sub th/), differential gain (dg/dN), and relaxation resonance frequency per square root of output power (fr/(P)/sup 1/2/) of the 1.55-/spl mu/m bulk DFB LD are 19 mA, 2.4/spl times/10/sup -16/ cm/sup 2/, and 3.2 GHz/mW/sup 1/2/, which nearly agree with the calculated I/sub th/ of 21.6 mA, dg/dN of 3.1/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 3.6 GHz/mW/sup 1/2/, respectively. The experimentally obtained I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m InGaAs MQW DFB LD with barriers (/spl lambda/g=1.3 /spl mu/m) are 9 mA, 6.0/spl times/10/sup -16/ cm/sup 2/, and 4.6 GHz/mW/sup 1/2/ compared with the calculated I/sub th/ of 7.8 mA, dg/dN of 4.0/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 3.7 GHz/mW/sup 1/2/, respectively. However, the experimentally obtained I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m InGaAs MQW DFB LD with barriers (/spl lambda/g=1.15 /spl mu/m) are 20 mA, 2.6/spl times/10/sup -16/ cm/sup 2/, and 2.85 GHz/mW/sup 1/2/, which greatly disagree with the calculated I/sub th/, of 4.9 mA, dg/dN of 6.0/spl times/10/sup -16/ cm/sup 2/, and fr/(P)/sup 1/2/ of 4.3 GHz/mW/sup 1/2/, respectively. Taking into account the nonuniform hole distribution among nine wells, which is attributed to the valence band discontinuity, /spl Delta/E/spl upsi/ (the separation between the first quantized hole level in the well and the top energy of the valence band for the barrier), the corrected I/sub th/ and dg/dN of the 1.55-/spl mu/m MQW DFB LD with /spl lambda/g of 1.15 /spl mu/m are 18.3 mA and 2.2/spl times/10/sup -16/ cm/sup 2/, which fairly agree with the above measured values. By p-type doping to 1.5/spl times/10/sup 18/ cm/sup -3/ into the wells to improve the nonuniform distribution of holes among nine wells, I/sub th/, dg/dN, and fr/(P)/sup 1/2/ of the 1.55-/spl mu/m MQW DFB LD with /spl lambda/g of 1.15 /spl mu/m can be expected to be 3.7 mA, 8.8/spl times/10/sup -16/ cm/sup 2/, and 5.4 GHz/mW/sup 1/2/, respectively.