Luminescence decay kinetics in GaP:Bi and GaP:N

The lifetime of excitons bound to isoelectronic traps in GaP is studied as a function of temperature, excitation energy and intensity. The photoluminescence was excited both selectively and above the gap by using a pulsed, tunable dye laser with photon flux varying in the range of 10¹⁴–10¹⁹ photons/cm² per pulse. GaP:Bi shows a strong intensity dependence of τ(T) in the temperature range of 40–60 K due to the thermal activation of the electron. Similarly, GaP:N shows this behavior in the range of 20–100 K. In this case, two activation processes can be identified: release of the bound exciton into the free exciton band and dissociation of the exciton. The observed dependence of τ(T) on both excitation energy and intensity indicate that saturable deep traps (shunt paths) deplete the excess free carriers. These traps can be completely saturated in GaP:N while only partial saturation is achieved in GaP:Bi. The kinetic equations are written for GaP:Bi and solved numerically assuming quasiequilibrium conditions. Fitting this model to the experimental results yields the capture cross sections for carriers by Bi and by the deep traps as well as the concentration of the latter.     

A novel etching technology with reactive ion etching system for GaAs via-hole etching applications

A via-hole dry etching technique has been studied with manipulating RF power and gas pressures in a reactive ion etching system. These parameters were optimized into a two-step recipe. With the recipe, a sloped and smooth profile can be obtained for monolithic microwave integrated circuits and power FET applications. With the two-step etching recipe, greater than 25:1 selectivity between GaAs/photoresist and less than 10% etching deviation were obtained. Furthermore, the slope angle from the horizontal surface is less than 80/spl deg/.     

Uniform deposition of GaAs in a multiwafer vapor-phase epitaxial system

The growth of expitaxial GaAs layers with complex doping structures in a multiple-wafer chloride-transport vapor-phase epitaxial system is reported. The use of kinetically limited growth in a 4-in-diam reaction chamber permits deposition on multiple large substrates with doping and thickness variations less than ±5.5 and ±8 percent, respectively. Solid GaAs sources were used in order to eliminate the complications associated with the saturation of liquid Ga. State-of-the-art single- and double-drift IMPATT materials were grown in this reactor and fabricated devices demonstrated excellent RF performance. The results suggest that it is possible to produce device-quality GaAs in large quantities and at low cost on a routine basis using the well-developed chloride-transport method.     

Laser chemical etching of vias in GaAs

Rapid drilling of vias in thick wafers (381 µm) of GaAs has been achieved by a laser assisted etching process. The technique utilized a cw visible argon ion laser and an etchant gas of low pressure Cl2. Data on the dependence of the etch rate on the laser power, wavelength, and Cl2gas pressure are presented.     

Transition metal deep centers in GaAs,GaP and Si

A simple model predicts that the energy of a transition element relative to the valence band edge is related to elastic stress and therefore to the radius. This model has been originally applied to a few elements in GaAs, but is shown to give moderately quantitative results for a range of substitutional iron-group transition elements from Sc to Cu in GaAs and to a lesser extent between measurements and theory for GaP and Si. The radius term involved is of the form R_M²δR, where δR is the difference between the metal atom with a full 3d shell and the tetrahedral covalent radius of the atom with +2 coordination. Other transition metal properties, such as distribution coefficients and hole lifetimes also appear to be related to atomic radius, implying that impurity induced stresses may be involved.     

GaAs/GaP Quantum-Well Heterostructures Grown on Si Substrates

Semiconductors - Molecular-beam epitaxy is used to produce GaP/Si hybrid substrates that allow the growth of highly efficient light-emitting heterostructures with GaAs/GaP quantum wells. Despite...     

Growth of BGaAs layers on GaAs substrates by metal-organic vapor-phase epitaxy

B_xGa_1?xAs layers were grown on GaAs substrates using low-pressure metal-organic vapor-phase epitaxy. Triethylboron, trimethylgallium, and arsine were used as boron, gallium, and arsenic sources. Optimum growth conditions were selected. The layers were studied using X-ray diffraction, secondary-ion mass spectrometry (SIMS), and photocurrent spectroscopy (PCS). The SIMS results showed a uniform boron distribution over the layer thickness. According to the PCS data, the BGaAs band gap decreases as the boron concentration increases.     

Optoelectronic phenomena in GaAs and GaP layers prepared by nitrogen treatment

Plasma processing of single-crystal wafers of gallium arsenide and gallium phosphide is employed to obtain thin wideband layers. The spectral dependence of the photoluminescence of the layers and of the photosensitivity of the corresponding layer/substrate structures is investigated. An analysis of the results of these studies gives us reason to believe that the described process leads to replacement of arsenic and phosphorus atoms by nitrogen and to the formation of wideband layers of solid solutions on the surface of the indicated semiconductors. Fiz. Tekh. Poluprovodn. 32, 1203–1205 (October 1998)     

Impurity removal by chemical beam etching of GaAs

The effectiveness of the chemical beam etching process to remove dopant impurities from GaAs is investigated. Structures containing Si and Be δ-doped as well as uniformly Si-doped layers were subjected to etching and the dopant distributions were monitored by secondary ion mass spectrometry. While Be is shown to be promptly removed from GaAs by this technique, Si is shown to chemically react much less effectively to the etching process     

Ohmic contact formation during continuous heating of GaAs and GaP Shottky diodes

Changes in the current-voltage and capacitance-voltage characteristics of semiconductor-solid metal structures (GaAs-Ni and GaP-Au Schottky diodes) during continuous heating have been studied. It is shown that the rectifying contacts are transmuted into ohmic contacts at some temperature T _ohm. This transition precedes the possible formation of a recrystallized layer that is peculiar to conventional ohmic contacts. The transition temperature T _ohm is substantially lower than the melting point of the metal. The current-voltage characteristics of structures annealed at different temperatures T _ann and cooled to room temperature have been studied. It is shown that at some temperature T _ann lower than some critical temperature T ₀ the structural properties remain virtually constant, that at T _ohm>T _ann>T ₀ the structures remain rectifying but excess currents appear, and that at T _ann>T _ohm the structures become irreversibly ohmic. It is assumed that after chemical interaction between the metal and the surface layer of the semiconductor, the newly formed surface acquires properties that account for the ohmic characteristics of the metal-semiconductor contact. Fiz. Tekh. Poluprovodn. 32, 200–202 (February 1998)     

GaAs integrated optical circuits by wet chemical etching

An integrated optical circuit containing a laser, passive waveguide, and extra-cavity detector is described. These devices are fabricated from AlxGa1-xAs layers grown by liquid-phase epitaxy. Reflectors are formed by a two-step preferential etch procedure. For proper laser orientation on {100} wafers, the mirrors are found to be oblique, tapered so as to enhance coupling into the underlying passive waveguide; this increases the efficiency of radiation transfer to the detector. Device operation with high differential transfer efficiency and low threshold has been achieved; e.g., for devices with one etched mirror and one cleaved mirror, ηt= 16 percent andJ_{t} = 2.4kA/cm², whereas these values areeta_{t} = 6.5percent and Jt= 3.0 kA/cm²for devices with two etched mirrors. Other orientations on {100} and {110} wafers have also been investigated. The reflectivity of the etched mirrors is small,R_{e} simeq 1-2percent, but transfer efficiencies into the external passive waveguide as large asT = 50percent have been observed. The effect of small Reon device performance is examined both experimentally and theoretically. The fabrication of ribbed interconnections between active circuit components is also described.     

Quantum confinement of carriers in heterostructured GaAs/GaP quantum wires

We present theoretical calculations on the confinement of electrons and holes in a heterostructured GaAs/GaP quantum wires within the effective mass approximation. Energy levels (ground state and excited states), as well as electron-hole recombination energies for some transitions, are calculated for different combinations of wire radius, well widths, and interface thickness.     

Damage-free reactive ion etching of GaAs FET gate recess

A GaAs reactive ion etching process is described which has good uniformity and causes no significant electrical damage to the underlying substrate. The process is shown to be suitable for forming the gate recess of a GaAs MESFET. FETs fabricated using the process exhibit DC and RF performance similar to equivalent wet etched devices.<>     

GaAs PHEMT器件的失效模式及机理

归纳了GaAs PHEMT器件的几种常见失效模式,并从6个方面分析了PHEMT器件的失效机理:热电子应力退化、氢效应、2DEG结构退化、欧姆接触退化、肖特基接触退化和电迁移.     

Submicrometer gate fabrication of GaAs MESFET by plasma etching

Dry etching is employed in the direct fabrication of the main part of semiconductor devices. A submicrometer Schottky-barrier gate is constructed for GaAs MESFET's. The gate has a double-metal-layer configuration. The Au top metal layer is first delineated by ion milling with monitoring equipment, i.e., ion microanalyzer. The metal layer in contact with the GaAs substrate is chemically etched in CF4gas plasma. Controlled side etching of the Mo metal produces the submicrometer gate, leaving a wider top metal layer of Au. The amount of side etching deviates less than 0.05 µm and the gate length is reduced to 0.1 µm. No appreciable damage to the GaAs substrate is found as a result of plasma etching. Half-micrometer gate GaAs MESFET's fabricated by this dry etching technique achieved high-gain and low-noise performance in the X-band.     

The preparation and characterization of strained-layer superlattices in the GaAs + GaP System

The technique of metal organic chemical vapor deposi-tion has been used to prepare strained-layer superlattices in the GaAs + GaP system. The superlattices consist of alternating layers of GaP and GaAs_xP_1?x for x = 0.2 to 1.0, which vary in thickness from 30 to 400 Å. The layers were grown by the decomposition of trlmethylgallium and various mixtures of ASH₃ and PH₃ in H₂ at 800δC. The thickness and uniformity of the layers were determined by optical and transmission electron microscopy and x-ray diffraction. The composition of the layers was determined from x-ray diffraction. A new analysis has been developed to determine the layer strain as well as the composition of thick layers (～ 300 Å). Transmission electron microscopy has been used to yield direct evidence that strained-layer superlattices can be used to remove the misfit dislocations generated during the epitaxial growth of a GaAs_xP_1-x alloy on a lattice mismatched GaP substrate. These results are in agreement with the previous work of Matthews and Blakeslee. Optical absorption, photocurrent spectroscopy and photoluminescence have been used to deter-mine the band gap energy as well as the energies for other optical transitions. The values are in excellent agreement with the values predicted by tight binding and effective mass calculations.     

Cl2 chemical dry etching of GaAs under high vacuum conditions—Crystallographic etching and its mechanism

Cl₂ chemical dry etching for GaAs substrates of {111}A, {111}B, {110} and {100} orientations was accomplished under high vacuum conditions. The etch rate for different substrate orientations was {111}B > {110} = {100} > {111}A for temperatures below 450° C, and was nearly equal for temperatures above 450° C. For {111}B, {110} and {100} substrates, the etch rate depends strongly on the substrate temperature above 450° C and below 150° C. Two activation energies for etching (10.0 kcal/mol below 150° C and 16.0 kcal/mol above 450° C) were obtained. Between 150 and 450° C, the etch rate depends weakly on the substrate temperature. However, for {111}A substrate, the etch rate increased monotonically with increasing substrate temperature above 300° C. The activation energy corresponds to that for the other substrates above 450° C. These results are caused by the surface chemical reaction of GaAs/Cl₂. By using these etching properties, a vertical side wall was fabricated without ion bombardment.     

Volatile component loss and contact resistance of metals on GaAs and GaP during annealing

This work is devoted to a mass spectrometric study of volatile component loss and in situ measurement of the resistance of metallized GaAs and GaP samples during heat treatment. Arsenic losses during heat treatment have been determined quantitatively with a quadrupole mass spectrometer. A relation was found between the arsenic loss and the specific contact resistance of the metallized sample. The associated activation energy was found to be similar to the case of thin film diffusion.     

Segregation of indium in InGaAs/GaAs quantum wells grown by vapor-phase epitaxy

Distribution of indium atoms in structures which contained double InGaAs/GaAs quantum wells and were grown by vapor-phase epitaxy from metal-organic compounds was studied. Experimental indium-concentration profiles were obtained using Auger electron spectroscopy. A model of growth with allowance made for indium segregation and a model for the Auger profiling were used in the calculations of profiles. Fitting calculated profiles to experimental ones made it possible to estimate the activation energies for In-Ga exchange in the context of a kinetic model for segregation. These energies are found to be somewhat higher than those that are well known for molecular-beam epitaxy, which is related to stabilization of the growth surface by hydrogen atoms in a vapor-phase reactor.