Quantum transport measurements on Si δ- and slab-doped In0.53Ga0.47As grown by molecular beam epitaxy

A series of high quality δ-doped In_0.53Ga_0.47As samples have been grown lattice matched to InP with design doping densities in the range 2×10¹² to 5×10¹² cm⁻². Analysis of the individual sub-band densities deduced from the Shubnikov-De Haas effect shows that both spreading and amphoteric behaviour increase with doping density.     

The role of hydrogen in low-temperature MOVPE growth and carbon doping of In0.53Ga0.47As for InP-based HBT

Hydrogen radicals are decisive for the low-temperature growth and carbon doping of In_0.53Ga_0.47As in LP-MOVPE. This is demonstrated for the growth of highly p-type doped In_0.53Ga_0.47As layers with CCl₄ as dopant source. Perturbed angular correlation measurements (PAC) were used to investigate the passivation of acceptors by hydrogen in low-temperature grown In_0.53Ga_0.47As. Based on the above analysis an InP-based layer stack is developed which employs low-temperature growth of the base layer, high-temperature growth of the remaining HBT layers, and an in situ post-growth annealing under TMAs/N₂ ambient.     

Structure and optical properties of self-assembled InAs/GaAs quantum dots with In0.15Ga0.85As underlying layer

A high density of 1.02×10¹¹ cm⁻² of InAs islands with In_0.15Ga_0.85As underlying layer has been achieved on GaAs (1 0 0) substrate by solid source molecular beam epitaxy. Atomic force microscopy and PL spectra show the size evolution of InAs islands. A 1.3 μm photoluminescence (PL) from InAs islands with In_0.15Ga_0.85As underlying layer and InGaAs strain-reduced layer has been obtained. Our results provide important information for optimizing the epitaxial structures of 1.3 μm wavelength quantum dots devices.     

Low dark current In0.53Ga0.47As/InP SAM avalanche photodiodes grown by gas-source MBE

In_0.53Ga_0.47As/InP avalanche photodiodes (APDs) with separate absorption and multiplication (SAM) regions have been grown by gas-source molecular beam epitaxy (GSMBE). These mesa-structure diodes, with a mesa diameter of 150 μm, exhibit a very low dark current of 17 nA, and primary unmultiplied dark current of less than 1.0 nA at 90% of the breakdown voltage. A gain as high as 100 is observed near the breakdown. Good uniformities of punch-through voltage and breakdown voltage were obtained on a 16 mm×16 mm wafer. Also, a premature breakdown was observed in the In_0.53Ga_0.47As/InP SAM-APDs with a V-shaped defect density of 25,000 cm^-2.     

Heterointerface study of perturbed LPE growth of AlGaAs/InGaP single heterostructure

This paper presents the perturbed growth of Al_0.7Ga_0.3As/In_0.5Ga_0.5P single heterostructure on a GaAs substrate by liquid-phase epitaxy. The AlGaAs-InGaP heterointerface was characterized by scanning electron microscopy, photoluminescence, Auger electron spectroscopy, and transmission electron microscopy. Evidence is provided showing that a small amount of droplets, after the slider operation of the In_0.5Ga_0.5P epitaxial growth, mixed with the Ga-rich AlGaAs melt, is sufficient to attack the In_0.5Ga_0.5P underlying layer. Even with complete melt removal, there is still a partial dissolution at the “flat” Al_0.7Ga_0.3As-In_0.5Ga_0.5P heterojunction. The Auger depth profiles reveal the composition-depth transition width at this interface to be 560Å from the 90%-10% of Al (or Ga, As, and In) Auger profile; however, the P atoms penetrate deeply into the Al_0.7Ga_0.3As layer due to the partial dissolution of In_0.5Ga_0.5P layer. By high-resolution electron-micrograph analysis, some dislocations are observed at the heterojunction leading to nonradiative recombination and to poor optical device performance, even though the heterointerface observed by scanning electron microscopy is very flat.     

Heavily carbon-doped p-type InGaAs by MOMBE

Carbon-doped In_xGa_1−xAs layers (x=0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As₄) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x=0.8. Hole concentrations of 1.0×10¹⁹ and 1.2×10¹⁸ cm^-3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In_xGa_1−xAs by MBE. Preliminary results on carbon-doped GaAs/In_xGa_1−xAs strained layer superlattices are also discussed.     

Heavily carbon-doped p-type (In)GaAs grown by gas-source molecular beam epitaxy using diiodomethane

Heavily carbon-doped p-type In_xGa_1−xAs (0≤x<0.49) was successfully grown by gas-source molecular beam epitaxy using diiodomethane (CH₂I₂), triethylindium (TEIn), triethylgallium (TEGa) and AsH₃. Hole concentrations as high as 2.1×10²⁰ cm⁻³ were achieved in GaAs at an electrical activation efficiency of 100%. For In_xGa_1−xAs, both the hole and the atomic carbon concentrations gradually decreased as the InAs mole fraction, x, increased from 0.41 to 0.49. Hole concentrations of 5.1×10¹⁸ and 1.5×10¹⁹ cm⁻³ for x = 0.49 and x = 0.41, respectively, were obtained by a preliminary experiment. After post-growth annealing (500°C, 5 min under As₄ pressure), the hole concentration increased to 6.2×10¹⁸ cm⁻³ for x = 0.49, probably due to the activation of hydrogen-passivated carbon accepters.     

Structural and photoluminescence characteristics of molecular beam epitaxy-grown vertically aligned In0.33Ga0.67As/GaAs quantum dots

In this paper, we present the results of structural and photoluminescence (PL) studies on vertically aligned, 20-period In_0.33Ga_0.67As/GaAs quantum dot stacks, grown by molecular beam epitaxy (MBE). Two different In_0.33Ga_0.67As/GaAs quantum dot stacks were compared. In one case, the In_0.33Ga_0.67As layer thickness was chosen to be just above its transition thickness, and in the other case, the In_0.33Ga_0.67As layer thickness was chosen to be 30% larger than its transition thickness. The 2D–3D growth mode transition time was determined using reflection high-energy electron diffraction (RHEED). Structural studies were done on these samples using high-resolution X-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (XTEM). A careful analysis showed that the satellite peaks recorded in X-ray rocking curve show two types of periodicities in one sample. We attribute this additional periodicity to the presence of an aligned vertical stack of quantum dots. We also show that the additional periodicity is not significant in a sample in which the quantum dots are not prominently formed. By analyzing the X-ray rocking curve in conjunction with RHEED and PL, we have estimated the structural parameters of the quantum dot stack. These parameters agree well with those obtained from XTEM measurements.     

Chemical beam epitaxy of AlGaAs and AlInAs using trimethylamine alane precursor

Al_xGa_1−xAs and Al_xIn_1−xAs alloys were grown on GaAs and InP, respectively, by chemical beam epitaxy, using trimethylamine alane (TMAA) as the source of aluminium. TMAA could be used properly only after some problems had been solved. Low carbon and oxygen concentrations were obtained in both alloys, leading to residual hole concentrations of 2 × 10¹⁶ cm^-3 in Al_0.3Ga_0.7As. The abruptness of the AlGaAs/GaAs interface proved the absence of TMAA memory effect. The control of Al_xIn_1−xAs solid composition was more difficult than for Ga_xIn_1−xAs, but was less sensitive to growth temperature. Photoluminescence intensities of Al_0.3Ga_0.7As and Al_0.48In_0.52As grown at 510°C were similar to those of MBE grown materials.     

Growth and MBMS studies of reaction mechanisms for InxGa1−xAs CBE

The reaction mechanism involved in the growth of In_xGa_1−xAs lattice matched to InP by chemical beam epitaxy (CBE) was investigated using growth and modulated beam mass spectrometry studies. Emphasis was placed on elucidating how variations in substrate temperature, indium composition and arsenic overpressure influence growth kinetics and how sensitive changes in experimental conditions bring about deviations in the ideal stoichiometry (In_0.53Ga_0.47As) required for lattice matching to InP. Our observations indicate that the compositional variations in the InGaAs stoichiometry at high temperatures (> 485°C) arise because of the changes in the DEG decomposition: desorption branching ratio which is controlled by a temperature- and arsenic pressure-dependent surface population of indium atoms. The low temperature behaviour is governed by the availability of metal surface sites for triethylgallium decomposition which is increased by the presence of surface indium atoms.     

Se-doped AlGaAs grown on GaAs(111)A by molecular beam epitaxy

The electrical properties of Se-doped Al_0.3Ga_0.7As layers grown by molecular beam epitaxy (MBE) on GaAs(111)A substrates have been investigated by Hall-effect and deep level transient spectroscopy (DLTS) measurements. In Se-doped GaAs layers, the carrier concentration depends on the misorientation angle of the substrates; it decreases drastically on the exact (111)A surface due to the re-evaporation of Se atoms. By contrast, in Se-doped AlGaAs layers, the decrease is not observed even on exact oriented (111)A. This is caused by the suppression of the re-evaporation of Se atoms, by Se---Al bonds formed during the Se-doped AlGaAs growth. An AlGaAs/GaAs high electron mobility transistor (HEMT) structure has been grown. The Hall mobility of the sample on a (111)A 5° off substrate is 5.9×10⁴ cm²/V·s at 77 K. This result shows that using Se as the n-type dopant is effective in fabricating devices on GaAs(111)A.     

InGaAs---GaAs pseudomorphic heterostructure transistors prepared by MOVPE

In this paper, we will demonstrate two new InGaAs-GaAs pseudomorphic heterostructure transistors prepared by MOVPE technology, i.e. InGaAs-GaAs graded-concentration doping-channel MIS-like field effect transistors (FET) and heterostructure-emitter and heterostructure-base (InGaAs-GaAs) transistors (HEHBT). For the doping-channel MIS-like FET, the graded In_0.15Ga_0.85As doping-channel structure is employed as the active channel. For a 0.8 × 100 μm² gate device, a breakdown voltage of 15 V, a maximum transconductance of 200 mS/mm, and a maximum drain saturation current of 735 mA/mm are obtained. For the HEHBT, the confinement effect for holes is enhanced owing to the presence of GaAs/InGaAs/GaAs quantum wells. Thus, the emitter injection efficiency is increased and a high current gain can be obtained. Also, due to the lower surface recombination velocity of InGaAs base layers, the potential spike of the emitter-base (E-B) junction can be reduced significantly. This can provide a lower collector-emitter offset voltage. For an emitter area of 4.9 × 10⁻⁵ cm², the common emitter current gain of 120 and the collector-emitter offset voltage of 100 mV are obtained.     

Investigations on the effect of InSb and InAsSb step-graded buffer layers in InAs0.5Sb0.5 epilayers grown on GaAs (0 0 1)

We report the structural and electrical properties of InAsSb epilayers grown on GaAs (0 0 1) substrates with mid-alloy composition of 0.5. InSb buffer layer and InAs_xSb_1−x step-graded (SG) buffer layer have been used to relax lattice mismatch between the epilayer and substrate. A decrease in the full-width at half-maximum (FWHM) of the epilayer is observed with increasing the thickness of the InSb buffer layer. The surface morphology of the epilayer is found to change from 3D island growth to 2D growth and the electron mobility of the sample is increased from 5.2×10³ to 1.1×10⁴ cm²/V s by increasing the thickness of the SG layers. These results suggest that high crystalline quality and electron mobility of the InAs_0.5Sb_0.5 alloy can be achieved by the growth of thick SG InAsSb buffer layer accompanied with a thick InSb buffer layer. We have confirmed the improvement in the structural and electrical properties of the InAs_0.5Sb_0.5 epilayer by quantitative analysis of the epilayer having a 2.09 μm thick InSb buffer layer and 0.6 μm thickness of each SG layers.     

Growth by self-flux method and post-annealing effect of Bi2Sr2Ca1Cu2Ox single crystals

Post-annealing effects on superconducting characteristics have been studied in Bi₂Sr₂Ca₁Cu₂O_x single crystals grown by a conventional flux method. Also, favorable growth conditions and the effect of the pre-sintering process on the starting materials for flux growth have been examined. The best superconducting behavior is obtained in post-annealed crystals grown from pre-sintered powder materials. The critical current density J_c estimated from magnetization hysteresis in annealed crystals grown with pre-sintered materials is roughly 8×10⁵ A/cm² (Hc) and 5×10⁴ A/cm² (Hc) at 4.2 K at zero field.     

Influence of cooling rate on the liquid-phase epitaxial growth of Zn3P2

We report the liquid-phase epitaxial growth of Zn₃P₂ on InP (1 0 0) substrates by conventional horizontal sliding boat system using 100% In solvent. Different cooling rates of 0.2–1.0 °C/min have been adopted and the influence of supercooling on the properties of the grown epilayers is analyzed. The crystal structure and quality of the grown epilayers have been studied by X-ray diffraction and high-resolution X-ray rocking measurements, which revealed a good lattice matching between the epilayers and the substrate. The supercooling-induced morphologies and composition of the epilayers were studied by scanning electron microscopy and energy dispersive X-ray analysis. The growth rate has been calculated and found that there exists a linear dependence between the growth rate and the cooling rate. Hall measurements showed that the grown layers are unintentionally doped p-type with a carrier mobility as high as 450 cm²/V s and a carrier concentration of 2.81×10¹⁸ cm⁻³ for the layers grown from 6 °C supercooled melt from the cooling rate of 0.4 °C/min.     

Critical layer thickness of In0.82Ga0.18As/InP quantum wells

We present results on a study of strained In_0.82Ga_0.18As/InP quantum wells (QWs) grown by gas source MBE. From transmission electron microscopy, we find that the onset of dislocation creation occurs for thickness around 60 Å. Strain release is found to induce a dramatic effect on the carrier lifetime as shown by time-resolved photoluminescence technique: lifetimes values of 2 ns are measured on QWs with thickness of 18 and 40 Å, but drop to 60 ps on a 64 Å thick QW.     

SiC epitaxial layer growth in a novel multi-wafer vapor-phase epitaxial (VPE) reactor

Experimental results are presented for SiC epitaxial layer growths employing a unique planetary SiC-VPE reactor. The high-throughput, multi-wafer (7×2″) reactor, was designed for atmospheric and reduced pressure operation at temperatures up to and exceeding 1600°C. Specular epitaxial layers have been grown in the reactor at growth rates ranging from 3–5 μm/h. The thickest layer grown to date is 42 μm thick. The layers exhibit minimum unintentional n-type doping of 1×10¹⁵ cm⁻³, and room temperature mobilities of 1000 cm²/V s. Intentional n-type doping from 5×10¹⁵ cm⁻³ to >1×10¹⁹ cm⁻³ has been achieved. Intrawafer layer thickness and doping uniformities (standard deviation/mean at 1×10¹⁶ cm⁻³) are typically 4 and 7%, respectively, on 35 mm diameter substrates. Moderately doped, 4×10¹⁷ cm⁻³, layers, exhibit 3% doping uniformity. Recently, 3% thickness and 10% doping uniformity (at 1×10¹⁶ cm⁻³) has been demonstrated on 50 mm substrates. Within a run, wafer-to-wafer thickness deviation averages 9%. Doping variation, initially ranging as much as a factor of two from the highest to the lowest doped wafer, has been reduced to 13% at 1×10¹⁶ cm⁻³, by reducing susceptor temperature nonuniformity and eliminating exposed susceptor graphite. Ongoing developments intended to further improve layer uniformity and run-to-run reproducibility, are also presented.     

CBE growth of high-quality AlGaAs/GaAs heterostructures for HEMT applications

AlGaAs/GaAs heterostructures were grown by chemical beam epitaxy using triethylgallium, triisobutylaluminium and pure arsine in flow control mode with hydrogen as carrier gas. For substrate temperatures of 580°C and V/III ratios of 10, high quality AlGaAs layers are obtained; heterostructures show abrupt and smooth interfaces. Modulation doping with silicon evaporated from a conventional effusion cell gives two-dimensional electron gases with carrier densities up to 1×10¹² cm^-2. Mobilities of 70000 cm²/V·s are obtained at 77 K for carrier densities of 4×10¹¹ cm^-2. The lateral homogeneity of the heterostructures in layer thickness, composition and doping level is excellent. Perfect morphology with defect densities of about 100 cm^-2 is observed. High electron mobility transistors (gate length 0.3 nm) fabricated from quantum well structures show a transconductance of about 380 mS/mm.     

Formation of oxygen-deficient type structural defects and state of ions in SiO2 glasses implanted with transition metal ions

The properties and concentrations of oxygen-deficient type structural defects in type III SiO₂ glasses implanted with Ti⁺, Cr⁺, Mn⁺, Fe⁺, or Cu⁺ to doses from 0.5×10¹⁶ to 6×100¹⁶ ions/cm² at an energy of 160 keV have been measured by using vacuum UV and EPR spectroscopies. An intense absorption band centered around 7.5 eV is observed in all the samples except for Cu-implanted ones and is attributed primarily to Si---Si homo-bonds with the bond distance close to that of the Si₂H₆ molecule. The homo-bond and implanted ion concentrations are of the same order of magnitude in the implanted layers. An E′ type center associated with the homo-bond is observed in all the samples except for Cu-implanted ones. Anomalous behaviors of the Cu-implanted samples are attributed to the formation of Cu-colloids. An enhanced formation of metallic particles or colloids is suggested for the samples implanted with Cr, Mn or Fe to doses higher than 3×10¹⁶ ions/cm².     

Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH3, and Si2H6

High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI₂H₆ (n = 9 × 10¹⁷ cm^-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 10¹⁹ cm^-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 10⁴ A/cm². The device characteristics of our carbon-doped HBTs were found to be stable under current stress.