Comparative Study Of GaAs Research Articles

Comparative study of GaAs and CdTe solar cell performance under low-intensity light irradiance

Comparative study of GaAs and CdTe solar cell under low-intensity light irradiance was carried out to study the cell device performance in response to the changed light irradiance intensity. For highly efficient GaAs solar cell, the series Rs and the shunt Rp resistance were found to be low/high enough to have almost undetectable negative effect on the cell device performance at low-intensity light irradiance. The robust diode parameters guaranteed good cell performance at low-intensity light irradiance. An ideal logarithmic function was established to describe the variation of cell efficiency with light irradiance intensity for GaAs solar cell. For CdTe polycrystalline solar cell, the relatively large series resistance Rs and small shunt resistance Rp, compared to that of the GaAs solar cell, significantly decreased the cell fill factor. With increased light illumination intensity, both the diode ideality factor A and the reverse saturation current density J0 were increased due to the high density of interface states at the CdS/CdTe junction. The comparative study and conclusions drawn in this work provide device fabrication improvement direction for the CdTe solar cell.

Comparative study of GaAs and GaInNAs/GaAs multi-quantum well solar cells

Current–voltage (I–V) characteristics together with spectral quantum efficiency (QE) measurements are performed on a GaAs control and GaInNAs/GaAs multi-quantum well (MQW) solar cell under illumination with the AM1.5G spectrum. Nitrogen and Indium composition in the GaInNAs wells were selected as to ensure lattice matching to GaAs. The wells are shown to extend the spectral response to longer wavelengths but also cause a reduction in the QE at wavelengths below the GaAs band gap. Furthermore, the addition of wells generally causes a large decrease in open circuit voltage due to the increased dark current. The MQW cell reaches an efficiency of 5% compared to 8.5% for the GaAs control cell.

In situ study of GaAs growth mechanisms using tri-methyl gallium and tri-ethyl gallium precursors in metal-organic vapour phase epitaxy

A comparative study of GaAs (0 0 1) growth from tri-methyl gallium (TMGa) and tri-ethyl gallium (TEGa) was performed in metal-organic vapour phase epitaxy. The growth surfaces were characterised by reflectance anisotropy spectroscopy (RAS). Three distinct shapes of the RAS spectra typical for certain growth parameter regions were observed for both precursors. The RAS spectra typical for the growth at low temperatures correspond to kinetic limited growth and the surface is covered by adsorbates. At slightly higher temperatures in mass transport limited growth mode, a more gallium-rich surface appears with both precursors. In the case of TEGa, the lack of arsenic on the surface below 500°C is simply due to the lack of decomposed AsH 3. However, using TMGa gallium-rich surfaces are already found below 600°C. We propose steric hindrance of As diffusion by methyl groups around the incorporation sites and forced arsenic desorption by the formation of methyl arsine as the cause. At typical buffer growth temperatures above 600°C, the surfaces during growth are identical to the AsH 3 stabilised arsenic-rich pre-growth surfaces for both gallium precursors.

A comparative study of GaAs- and InP-based superlattice emitter resonant tunneling bipolar transistors (SE-RTBT's)

The InP/InGaAs and InGaP/GaAs superlattice emitter resonant tunneling bipolar transistors (SE-RTBTs) have been fabricated and demonstrated. By the employment of five-period superlattice in the emitter layer, the RT effect in saturation regime is observed at 77 K for InP/InGaAs SE-RTBT. In addition, due to the larger valence band discontinuity ΔE V at InGaP/GaAs heterojunction, the RT effect is observed both in saturation and forward active regimes at 300 K for InGaP/GaAs SE-RTBT. The confinement effect for minority carriers is enhanced due to the insertion of superlattice. The common emitter current gains up to 170 and 220 are observed for InP/InGaAs and InGaP/GaAs SE-RTBTs, respectively. Lower offset voltages of about 125 mV are observed in the studied devices.

A comparative study of GaAs- and InP-based HBT growth by means of LP-MOVPE using conventional and non gaseous sources

Low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) growth of carbon doped (InGa)P/GaAs and InP/(InGa)As heterojunction bipolar transistors (HBT) is presented using a non-gaseous source (ngs-) process. Liquid precursors TBAs/TBP for the group-V and DitBuSi/CBr 4 for the group-IV dopant sources are compared to the conventional hydrides AsH 3/PH 3 and dopant sources Si 2H 6/CCl 4 while using TMIn/TEGa in both cases. The thermal decomposition of the non gaseous sources fits much better to the need of low temperature growth for the application of carbon doped HBT. The doping behavior using DitBuSi/CBr 4 is studied by van der Pauw Hall measurements and will be compared to the results using Si 2H 6/CCl 4. Detailed high resolution X-ray diffraction (HRXRD) analysis based on 004 and 002 reflection measurements supported by simulations using BEDE RADS simulator enable a non-destructive layer stack characterization. InGaP/GaAs HBT structures designed for rf-applications are grown at a constant growth temperature of T gr=600°C and at a constant V/III-ratio of 10 for all GaAs layers. P-type carbon concentrations up to p = 5·10 19cm −3 and n-type doping concentrations up to n = 7·10 18cm −3 are achieved. The non self-aligned devices (A E = 3·10 μm 2)_show excellent performance, like a dc-current gain of B max = 80, a turn on voltage of V offset = 110 mV (Breakdown Voltage V CEBr,0 > 10 V), and radio frequency properties of f T/f max = 65 GHz/59 GHz. In the non-gaseous source configuration the strong reduction in the differences of V/III-ratios and temperatures during HBT structure growth enable easier LP-MOVPE process control. This is also found for the growth InP/InGaAs HBT where a high dc-current gain and high transit frequency of f T= 120 GHz are achieved.

Corrosion of III–V compounds; a comparative study of GaAs and InP: II. Reaction scheme and influence of surface properties

The paper presents a detailed reaction model for the corrosion of III–V compounds which quantitatively represents the experimental data (mainly Tafel plots of current vs. band displacement), presented in Part I J. Electroanal. Chem. Such data allow the discrimination between different reaction schemes. From a physical point of view, the model shows clearly that the differences observed between GaAs and InP arise from their different electronic surface properties. From a chemical point of view, a chemical signature of the corrosion states of GaAs is proposed: the states E C −0.98 eV and E C −1.15 eV, previously derived from photocapacitance spectroscopy, Ber. Bunsenges. Phys. Chem. 92 (1988) 895, could be associated with As sites and Ga sites, respectively. An analogous description holds for InP, with different positions of states. Within the framework of these original data, corrosion can be described by a first hole capture process on the cation site which becomes an anion site by the liberation of the cation. A chemical reaction step occurs before the second hole capture proceeds to dissolve the anion-related defect. Such a description is predicted by thermodynamical data and is further sustained by experimental facts such as the well-known As enrichment of GaAs surface in acidic media.

Corrosion of III-V compounds; a comparative study of GaAs and InP: Part I. Electrochemical characterization based on Tafel plot measurements

The kinetics and mechanism of corrosion of GaAs and InP have been investigated quantitatively by means of a combined experimental approach based principally on (i) Tafel plot measurements and (ii) the comparison of n- and p-type electrodes of the same material. In this work (Part I), the motivations and the limit of validity of this approach are discussed in detail along with the description of experimental results. It is shown that an extensive determination of the flat band potential under various electrochemical conditions (called in the following “Tafel plot recording” by analogy with metal substrates) is a very powerful technique, sensitive to a number of parameters of the contact such as (i) the pH of the solution, (ii) the doping density of the electrode, (iii) the type of electrode conduction (n-or p-type) and naturally (iv) the material itself. The present work brings new insight into electrochemical studies of the semiconductor/electrolyte junction and makes a parallel with the electrochemistry with metal electrodes. This part presents only the results. Part II will cover the discussion in relation to the surface electrochemical and chemical properties of GaAs and InP.

Summary Abstract: Comparative study of GaAs(111) and GaAs(1̄1̄1̄) surface reconstructions

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Current-voltage characteristics, small-signal parameters, and switching times of GaAs FET's

A new two-dimensional model of a GaAs FET is proposed. The model takes into account diffusion processes and Gunn-domain formation under the gate but it requires a very small computer time. The electric-field profiles under the gate, current-voltage characteristics, the dependences of the transconductance and gate-to-source capacitance on the drain voltage, and the dependences of a characteristic switching time and power-delay product on the device thickness are calculated. The results of the calculation agree well with the experimental data found earlier by other authors. The proposed model can be used for a computer-aided design of GaAs FET amplifiers and logic elements and also for a comparative study of GaAs and InP MESFET's.