We review Gas Source Molecular Beam Epitaxy of the GaAs/AlGaAs system. Among the growing number of condensed matter discoveries in materials grown by this approach we describe within resonant tunneling structures. This example serves to demonstrate the high quality quantum well formation and suppressed rate of dopant segregation that occurs during the GSMBE approach. We find a physical basis to quantify the latter growth effects when dopant segregation is viewed in two new ways. First, the broken translational symmetry created by the surface leads to dopant motion (as segregation) that otherwise is not allowed in the crystal interior (as diffusion). Secondly, dopants can dimerize on the crystal surface and this ultimately dictates how the rates of incorporation and segregation proceeds. The manner in which growth creates or destroyes covalent bonds of dopants on semiconductor surfaces thus presents new opportunities to improve dopant control.

Shubnikov-de Haas and Hall measurements have been performed on singly delta doped GaAs(Si) structures, grown by molecular beam epitaxy, enabling us to study the effects of illumination and temperature upon bulk and individual subband, mobilities and carrier concentrations. In a highly doped sample, where the peak 3D electron concentration approaches 2×1019cm−3, we have observed novel changes in subband transport characteristics, not observed in the lower doped samples, which we attribute to the presence of DX centre phenomena. This paper explains the variations in individual subband transport properties due to a possible shift of the electronic wave functions contained in the potential well. This shift occurs due to a recombination-autoionization(R-A) process involving filled DX centres and free holes upon sample illumination at low temperatures.

The occupation of deep-level defects in semiconductors is investigated by delta-doping such impurities at a specified distance from the metallurgical boundary within Schottky diodes. Capacitance-voltage characteristics are analyzed using ID device simulation software. These characteristics change significantly depending on the deep-level energy and the sheet position. This new approach to deep-level analysis is applied to Schottky diodes on MBE-grown n-GaAs with a planar titanium doped sheet. At moderate Ti concentrations the well-known Ti acceptor level near Ec-0.2 eV governs the electrical properties. In addition, two other types of Ti defects are found.

We have measured the Shubnikov-de Haas effect and Quantum Hall effect on the AlxGa1−xSb/InAs quantum wells for the A1 composition (x) from 0.1 to 1.0 under the negative persistent photoconductivity (NPPC) conditions. It confirmed the prediction of ionized deep donor model that the NPPC effect is a general property for the materials containing ionized deep donors at low temperatures. The time-dependent recombination (electron capture) of the ionized deep donors has the similar property to that of DX centers. The saturated reduction of carrier concentration in the InAs well increases with increasing x, and rises steeply at about x=0.4. By comparing with the concentration of the DX center-like deep donor in the bulk AlxGa1−xSb, we believe that the ionized deep donors which cause the NPPC in the AlxGa1−xSb,/InAs QW's are the DX center-like deep donors in the AlxGa1−xSb layers.

We present results of a study on the effect of unprecracked arsine(AsH3) and trimethylgallium(TMGa) on carbon incorporation in UHVCVD(Ultra High Vacuum Chemical Vapor Deposition) grown GaAs epilayers on GaAs(100). Three distinct temperature-dependent regions of growth rates were identified as growth temperature was increased from 570 to 690°C. The growth rates were also strongly dependent on V/III ratio in a range of 5 to 30, which clearly indicates that the growth rate is determined by the amount of arsenic adsorbed on the surface at low V/III ratio and adsorption of TMGa or decomposition process at high V/III ratio. Hall concentration measurements and low temperature photoluminescence data show that the films are all p-type and their impurity concentrations are reduced by two orders of magnitude compared to those of epilayers grown by CBE(Chemical Beam Epitaxy) which employs TMGa and arsenic(precracked arsines) as source materials. Our results indicate that the hydrogen atoms dissociated from adsorbed arsine may remove hydrocarbon species resulting in a significant drop in hole concentration.

The variation of luminescence parameters with the tin dopant concentration is considered in GaAs epitaxial layers. It is shown that at typical growth conditions and absence of contamination the deep accepters are generated by self material so that the compensation coefficient (K=Na/Nd) of 0.25 is constant up to critical electron concentration of 2.1018cm−3. The self-compensation is realized by native point defect ofattice which is gallium vacancy. The gallium vacancy is arranged next to the every fourth donor at the distance of 7 A.

We report on the first growth of GaAs/Ga0.5In0.5P heterostructures by conventional molecular beam epitaxy using solid-source valved crackers to supply both the arsenic and the phosphorus fluxes. By regulating the group V fluxes with the cracker needle valves, arsenide-phosphide heterostructures were successfully grown with virtually no group V intermixing between layers. For comparison, similar heterostructure samples were grown using only the mechanical shutters to switch between group V fluxes, and the resulting layers were severely intermixed. The amount of group V intermixing was shown to be independent of whether As2 or As4 fluxes were used to grow the layers. A GaAs/Ga0.5In0.5P multiple quantum well sample was also grown using the valved crackers. Photoluminescence peaks were clearly observed from 40 Å, 80 Å, and 300 Å GaAs quantum wells, but no luminescence was detected from a 20 Å well. An 80Å GaAs/ 80Å Ga0.5In0.5P superlattice was grown, and superlattice satellite peaks were observed in the X-ray rocking curves. The appearance of misfit dislocations suggests localized intermixing at the interfaces.

We study the effect of growth temperature (TG) and post-growth rapid thermal annealing (RTA) on the electrical properties of Schottky diodes fabricated on undoped, lattice-matched Ga0.51In0.49P/GaAs heterostructures. The samples were grown by metalorganic molecular beam epitaxy (MOMBE) in the temperature range 480 – 560°C. Ga0.51In0.49P grown in this temperature range undergoes spinodal decomposition, as shown by cross-section TEM analysis. The dislocation-free epilayers grown at TG≤520°C are characterized by a deep electron trap with an activation energy of 800meV while growth at higher temperatures renders trap-free films. Furthermore, the Schottky barrier ideality factor (n) depends strongly on TG and takes the best value of 1.4 for TG=540°C, while the barrier height remains nearly constant at about 0.75eV. Finally, upon capped rapid thermal annealing the value of n improves while the trap concentration decreases significantly. Based on the presented experimental evidence we can propose that MOMBE growth at 540°C renders films with improved electrical properties.

We report the observation of magnetic-field dependent excitonic photoluminescence energies and linewidths in ordered and disordered In0.48Ga0.52P alloys (lattice matched to GaAs). The photoluminescence measurements were made at 1.4 K and the applied magnetic field ranged between 0 and 13.6 tesla. With increasing magnetic fields, we observe increasing photoluminescence linewidths for disordered alloys and decreasing photoluminescence linewidths for the ordered alloys. The magnetic field dependence of the photoluminescence peak-energy shifts for all samples (ordered and disordered) is in good agreement with theoretical considerations. The presence of CuPt-type ordering was confirmed by transmission electron microscopy.

A reduction in the optical energy gap of more than 65 meV has been observed in In0.53Ga0.47 As grown on (100) InP by atmospheric pressure metalorganic vapor phase epitaxy. The band gap energies were deduced from room temperature photocurrent spectroscopic measurements, accounting for differences in composition and strain. Spontaneous CuPt type ordering of In and Ga atoms on the (111) subplanes of the InGaAs2 was confirmed by transmission electron microscopy. Superlattice signatures in the transmission micrographs were observed only for samples with associated reduced band gap energies, and were confirmed by visible double periodicity in high resolution images. In0.53Ga0.47 As was grown under a variety of conditions, some which promoted ordering. In general, lower growth temperatures and moderate (∼4 μ/hr) growth rates promoted a greater degree of ordering and reduction of the band gap energy. The influence of growth conditions on the ordered structure is considered within the context of current theories.

Data are presented showing the effect of As overpressure on the diffusion of Mn into an AlGaAs-GaAs superlattice (SL) using MnAs as the diffusion source. Arsenic overpressure has been shown to play a significant role in both impurity-induced layer disordering (IILD) and the microstructure of the Mn-diffused samples. The degree to which layer disordering occurs decreases as As overpressure increases. Furthermore, dislocation loops are observed for the diffusion of Mn under Ga-rich conditions at prolonged diffusion times. Both results, in addition to the effect of As overpressure on the Mn diffusion profile, indicate that Mn diffusion into GaAs or GaAs-AlGaAs heterostructures takes place by an interstitial-substitutional mechanism involving column III vacancies under As-rich conditions and a “kick-out” mechanism involving column III interstitials under Ga-rich conditions.

The ground state energy of a shallow impurity placed in the center of a circular quantum dot is studied. The effects of the strength of the confinement potential and a perpendicular magnetic field are investigated theoretically.

GaAs grown using Molecular Beam Epitaxy at below normal substrate temperatures (∼ 220 °C) has found many potential applications in GaAs MESFET devices. These so-called Low Temperature (LT) layers were originally used between the MESFET substrate and active region to eliminate backgating effects.[1] More recently, LT layers have been incorporated into MESFET gate structures to improve gate breakdown characteristics.[2] [3] When used in this capacity, the quality of the LT GaAs - n+ GaAs interface becomes an important issue: a large number of traps at the interface will result in channel mobility degradation. Furthermore, it is desirable to develop a method by which the interface quality can be evaluated through simple electrical measurements.

Silicon doped multiple quantum well (MQW) detector structures were rapid thermally processed (RTP) for the purpose of blue shifting the excitonic transition. Structures were encapsulated with Sio2 prior to the anneal as such enhanced the degree to which interdiffusion occurred within the structure. This further lead to a blue shift in the exciton energy corresponding to the n=l transition which was observed by photoluminescence (PL) measurements. Having examined the PL spectra of various SiO2 encapsulated samples and performing variable intensity PL measurements, a peak corresponding to a defect at ∼ 80meV above the valence band was further observed. In addition, a variation in the degree to which disordering occurs has been observed under various physical conditions including doping and GaAs capping.

It is a well-known phenomenon that the luminescence energies of nominally n monolayer (1 ML = 0.239 nm) thick QWs of GalnAs in InP are shifted to longer wavelengths in comparison to calculated values. The reason is seen in the formation of (Ga)InAs(P)-interfaces, one or a few ML thick, which contribute to the effective potential of the QW.Based on a comparison of MBE and MOVPE and on properties of QW structures grown by MOVPE under different conditions we conclude that high AsH3 pressures and low growth temperatures favour the formation of arsenic multilayers on the surface, which act as the main arsenic source for the formation of graded InAsxP1−x interface layers.

The interfacial structure of InGaAs/InP superlattices grown on (100) InP by metalorganic molecular beam epitaxy has been studied by fully dynamical simulations of high-resolution x-ray diffraction curves of the (200) and (400) reflectjon. The superlattice under investigation is lattice-matched and has a long period of ∼630Å. This kind of structure creates a very symmetrical x-ray pattern enveloping a large number of closely spaced satellite intensities with pronounced maxima and minima. It appears in the dynamical analysis that the position and shape of these maxima and minima is extremely sensitive to the number N of monolayers and atomic spacing d of the InGaAs and InP layer, as well as the presence of interfacial layers and impurities.

Interfaces in InGaAs/InP heterostructures were investigated by XAFS analysis using synchrotron radiation. Two types of InGaAs/InP heterostructures were made by MEE using Ga, In, AsH3 and PH3 as sources. These InGaAs layers were terminated by (a) InGa and (b) As. The local structures around P were investigated by fluorescent XAFS analysis. It shows that the nearest neighbor around P is Ga and In in the InGa (a) sample and mainly In in the As (b) sample.

In this paper we present contact-free measurement techniques which are important for the evaluation of heterojunctions of interest for optical as well as high-speed devices. The techniques are the microwave-detection of Shubnikov-de Haas oscillations, photoluminescence-detected magneto-oscillations, and optically detected cyclotron resonance using microwaves (ODCR) as well as far-infrared lasers (FIR-ODCR). The techniques are illustrated by several examples, and the possibilities to determine 2D carrier concentrations, effective masses, and scattering times in the heterojunction structures are discussed.

Photoreflectance (PR) has been performed on a series of undoped and n-type, InGaAs and InAlAs molecular beam epitaxy (MBE) grown layers with different In mole fractions, and epilayer thicknesses on Fe-doped semi-insulating (SI)-InP substrates. From investigations of the temperature dependence, time constant dependence and an additional cw light beam intensity dependence, three substrate peaks are identified as an excitonic transition from the substrate, a free electron transition near the interface which gives a Franz-Keldysh oscillation (KFO), and a transition from the spin-orbit split-off valence band. The results are indicative of a redistribution of charge near the substrate interface in the process of MBE growth; the associated PR signal (phase) could be used for in-situ monitoring of epilayer growth on SI-InP wafers.

The formation of mismatch dislocations in layered semiconductor structures was found recently in high resolution monochromatic synchrotron x-radiation diffraction images to be correlated with characteristics of the substrate as well as with the layer thickness and degree of lattice mismatch of non pseudomorphic layers.1,2 We have now extended these studies to examine the accommodation to strain as a function of lattice mismatch in a series of high electron mobility transistor (HEMT) structures grown by molecular beam epitaxy (MBE) on indium phosphide substrates.

Five distinct types of irregularity are observed: 1) lattice warping, 2) the formation of a nonpseudomorphic layer, 3) the formation of extended arrays of linear mismatch dislocations at the interface between the substrate and a nonpseudomorphic layer, 4) the formation of oval regions of tweed-like local lattice variation imbedded among these arrays, and 5) extended tweed-like local lattice variation over large peripheral areas in which the formation of straight mismatch dislocation arrays is not observed.

Warping of the lattice is found in nearly all layered structures. A distinct layer with a different lattice parameter but without visible misfit dislocations is formed with a mismatch of 0.27 %. With increase of the mismatch to 0.5 %, the other three forms of accommodation appear in distinct regions of the structure: arrays of <011> mismatch dislocations; oval regions of tweed-like irregularity, oriented in the [011] direction; and peripheral regions of extended tweed-like local lattice variation.