I. J. Fritz

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 GaAsxP1−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 GaAsxP1-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.

Long-wavelength, InAsSb strained-layer superlattice photovoltaic infrared detectors

Long-wavelength infrared photodiodes were fabricated using InAs/sub 1-x/Sb/sub x//InSb (x=0.82-0.85) strained-layer superlattices (SLSs). These structures can be grown using either molecular-beam epitaxy or metalorganic chemical vapor deposition. These photodiodes display broad spectral responses up to wavelengths greater than or approximately equal to 10 mu m, and detectivities of 1*10/sup 9/ cm-Hz/sup 1/2//W at 10 mu m.<<ETX>>

Doping and p-n function formation in InAs 1-x Sb x /InSb SLS's by MOCVD

Diethylzinc, dimethylcadmium, hydrogen selenide, silane, dimethyltellurium, and di-ethyltellurium were investigated as dopants for InSb and InAs1-xSbx. Carrier concentrations between 5 x 103 and 5 x 1019 cm-3 have been achieved for bothn- and p-type dopants by using dilute mixtures, 10 to 50 ppm, of dimethylcadmium and dimethyltellurium in hydrogen. The 77 K Hall mobilities of p-type InSb ranged from 7000 to 200 cm2/Vs and of n-type from 55,000 to 1700 cm2/Vs. An InAs0.17Sbo0.83/InSb SLS infrared photodiode has been fabricated with a wavelength response cutoff of 10.2 μm at 77 K. The zero bias, external current responsivity and infrared absorption of this device were measured. The predicted optical transitions using a type II heterojunction band offset closely match the observed absorption. The minority carrier diffusion length, perpendicular to the growth planes, is approximately 0.5 μm

Molecular beam epitaxy and characterization of Al x Ga 1– x As y Sb 1– y (0.0 ≤ x ≤ 1.0) lattice matched to InAs substrates

We report the molecular beam epitaxial growth of AlxGa1-xAsySb1-y (0.0 ≤ x ≤ 1.0) on undoped, liquid-encapsulated Czochralski, (100) oriented InAs substrates. The degree of lattice mismatch was determined by x-ray diffraction. The lattice matched materials (y ≈ 0.08 + 0.08x) were characterized by low temperature photoluminescence, electro-reflectance, and capacitance-voltage measurements. The experimental bandgap energies agree with earlier experimental results for AlxGa1-xSb, and also with a self-consistent first principles pseudopotential model. The capacitance-voltage measurements indicate background acceptor concentrations for the unintentionally-doped epitaxial layers of about 2 × 1015 cm-3 atx = 1.0 to 5 × 1016 cm-3 atx ≈ 0.0.

Semiconductor characterization by a new contactless electroreflectance technique employing surface acoustic waves

The interaction between an amplitude modulated surface acoustic wave on a piezoelectric substrate and the surface band bending and charge trapping at an adjacent semiconductor surface is employed to produce a modulated d.c. electric field in the near-surface region of the semiconductor. This field perturbs the optical reflectivity of the semiconductor, allowing derivative reflectance spectra to be obtained in a manner analogous to the familiar technique of photomodulated reflectance. This new contactless electroreflectance technique has been demonstrated by obtaining spectra, including structure above the bandgap, of (In)GaAs/AlGaAs multiple quantum well structures grown by molecular beam epitaxy.

Material characterization of an ion–implantation process for p-type (InGa)As/GaAs quantum–well structures

We have performed a detailed study of the formation of Be+-implanted contacts to modulation-doped, p-channel, (InGa)As/GaAs, single-strained quantum wells. Photoluminescence at 4 K from these structures is shown to be an excellent monitor of implant and annealing effects, as corroborated by Hall-effect measurements. Rapid thermal annealing produced higher electrical activation of the Be implants than did arsine-over-pressure annealing at comparable temperatures, similar to the trend in bulk GaAs. In contrast to conventional, alloyed-contact technologies, the rapid-annealed, implanted structures provided ohmic contact to the quantum well even at 4 K.

The growth of infrared antimonide-based semiconductor lasers by metal-organic chemical vapor deposition

We describe the metal-organic chemical vapor deposition (MOCVD) growth of InAsSb/InAs and GaAsSb/GaAs(P) multiple quantum well (MQW) and InAsSb/InAsP and InAsSb/InPSb strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. We also describe the growth and initial characterization of GaAsSbN/GaAs MQW structures. By changing the layer thickness and composition of the InAsSb SLSs and MQWs, we have prepared structures with low temperature (<20 K) photoluminescence wavelengths ranging from 3.2 to 6.0μ m. We have made gain-guided, injection lasers using undoped, p-type AlAs0.16Sb0.84 for optical confinement and both strained InAsSb/InAs MQW and InAsSb/InAsP and InPSb SLS active regions. The lasers and LEDs utilize the semi-metal properties of a p-GaAsSb/n-InAs heterojunction as a source for electrons injected into the active regions. Cascaded, semi-metal, mid-infrared, injection lasers with pseudomorphic InAsSb multiple quantum well active region lasers and LEDs are reported. We also report on GaAsSb/GaAs(P) lasers and LEDs emitting at 1.1 to 1.2 μm grown on GaAs substrates and using AlGaAs layers for confinement.

Effective masses and g factors for 2D light holes in InSb

The light holes in InSb are characterised using a Shubnikov-de Haas technique by exploiting the type II band offset of an InAs0.15Sb0.85/InSb strained-layer superlattice. The data are analysed to determine the effective masses and g factors as a function of carrier concentration.

Energy relaxation of light holes in InAs.15Sb.85/InSb multiple quantum wells

Abstract The energy relaxation rate of light in-plane holes in InAs .15 Sb .85 /InSb quantum wells has been measured using a Shubnikov-de Haas technique. In this Type II system, the holes reside in the InSb layers; strain reverses the heavy-light hole ordering and thus light holes are the charge carriers. The samples consist of 20 to 100 InAs .15 Sb .85 /InSb periods 100A/200A thick. The InAsSb barriers are doped with Be. The total carrier concentration p ≈ 1×10 11 cm −2 is obtained from Hall data. Shubnikov-de Haas oscillation amplitudes are measured and used to determine the light hole temperature for a given applied power. The steady state power per carrier is equated to the energy relaxation rate to determine the carrier temperature T H . The measured rate for low electric fields is proportional to T H n -T L n with n ≈ 3.2 and 2.5 for two different samples. These data are compared with theory and experiment for light holes in InGaAs/GaAs quantum wells.

High-field mobility of light holes in strained InGaAs quantum wells

Abstract The small in-plane mass of light holes in strained quantum wells leads to high mobility at low electric fields. An analysis shows that the high-field mobility in high quality samples primarily depends on Δ, the strain splitting of the light and heavy holes, and ħω 0 , the optical phonon energy. Monte Carlo calculations show that the carrier drift velocity versus electric field characteristic can be optimized for Δ ≈ ħω 0 . In this case, the low field mobility is enhanced but a Gunn effect is avoided at high fields. Pulsed field measurements on a p-doped GaAs/InGaAs/GaAs sample show that the drift velocity lies below the theoretical predictions. Further calculations in which interface roughness scattering is included show that interface roughness scattering can reduce the drift velocity. Comparison with the data suggests the roughness fluctuation length Δ ≈ 10 nm.