Lateral confinement of carriers and photons in semiconductor heterostructures is an important feature in modern electronic and optoelectronic devices. A number of techniques have been invented to induce lateral confinement with varying degrees of success and processing requirements. One of simplest but least commonly used technique is to utilize the strain induced effect (or the photoelastic effect) to cause confinement. While the concept is simple, the control of stress in the stressor layers is rather difficult in practice, without resorting to complicated selective growth of strained layers. We have investigated the controlled introduction of stable stresses into semiconductor heterostructures using a simple scheme of interfacial reactions between a metal and the substrate. Since the volumetric change for a given reaction is fixed, the induced stress in the structure is independent of the deposition method or the deposition system, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. We have made low-loss (~ ldB/cm at 1.53 μm) photoelastic waveguides in GaAs/AlGaAs and other layered structures by reacting Ni and other metals, with an underlying semiconductor. In the case Ni on GaAs/AlGaAs, the dominant stressor compound is N3GaAs, and the waveguide characteristics are thermally stable up to 600°C. Other photoelastic optical devices are also demonstrated.

We present a self-consistent field theory for the infrared absorption coefficient of a simple model of an array of narrow antiwires in an external magnetic field. A detailed study is made of the way in which the collective modes change from a cyclotron mode when the confining potential is weak, to tunneling coupled modes for intermediate antiwire potential strength, and then to edge and ID lattice magnetoplasmon modes for strong potentials. By using incident light with tunable frequencies in the interband excitation regime, contactless photoreflectance measurements may be carried out and the data compared with our calculations. By fitting the numerical results to the peak positions of the photoreflectance spectrum, the number of electrons in each wire may be extracted.

Crystalline nanometer-scale Ge particles have been synthesized by pulsed laser ablation and introduced into a Si host matrix, grown by chemical beam epitaxy from disilane. The proposed structure of the Ge:Si composite films consists of Ge nanocrystals surrounded by a thin epitaxial Si shell that passivates the surface of the Ge nanocrystallite. The Ge nanocrystallites are randomly oriented with respect to each other and are randomly distributed in a polycrystalline or amorphous Si matrix. Ge nanoparticles with and without Si matrix were deposited directly on C-coated TEM grid and imaged by high resolution TEM. Ge:Si composites deposited on Si wafers were characterized by RBS.

Numerous GaAs epitaxial microcrystals surrounded mainly by (111) and (110) facets having nearly equal size were grown on a sulfur(S)–terminated GaAs or GaALAs surface by sequentially supplying Ga and As molecular beams. The GaALAs layer growth over the GaAs microcrystals was performed by MEE process for burying GaAs microcrystals.

A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for synthesis of VI-II quantum dot composites. CdSe nanocrystallites dispersed in a mixture of pyridine and acetonitrile were electrosprayed into the gas-phase in the growth zone of an OMCVD reactor and then incorporated into a ZnSe matrix grown by OMCVD. Hydrogen selenide and diethylzinc were used to deposit the ZnSe matrix at temperatures of 150 - 240°C. The ZnSe/CdSe quantum dot composites were characterized by visible absorption spectroscopy, room temperature photoluminescence and Auger electron spectroscopy. The optical properties of the composites are determined by the size of the original CdSe nanocrystallites.

A laser ablation supersonic expansion source is used to deposit self-supporting thin films of agglomerated Si nanocrystallites. Average particle size is controlled through variation of deposition process parameters, including relative ablation pulse/gas valve timing and interaction channel length, as well as post-deposition processing steps, including repeated HF etch/oxide regrowth cycles, and oxidation furnace treatments. Films are characterized using photoluminescence (PL) emission spectroscopy. Clear spectral trends in the PL emission data point to a correlation between process parameter control, mean particle size, and peak PL wavelength. We conclude that quantum size effects play a critical role in defining the PL emission wavelength of Si nanocrystallites.

In0 53Ga0 47As layers were grown on (001 ) InP substrates by MOCVD. Growth conditions were chosen to optimize CuPt type LI1 ordering on the group III sublattice.

The surface morphology is shown to be strongly dependent on substrate degradation prior to growth. This degradation is highly dependent on temperature and initial gas flows. A survey of conditions leading to degradation as well as a safe method of initiating growth are given.

Films showing atomic ordering, as ascertained by cross sectional TEM, were examined by x-ray diffraction. A method of evaluating the structure factor for superlattice reflections is given. X-ray analysis was performed using a variation of the classical method of order parameter determination1. The order parameter is shown to vary with growth temperature and to have a maximum value of-0.21 at 550 C.

The transport properties of two device-related semiconductor microstructure quantum-well systems are addressed here. The first involves the theory of negative differential mini-band conductance (NDC) in a lateral semiconductor superlattice of very thin quantum dots laid out in a square array on a plane, both with and without a normal magnetic field. NDC of the total current is made steeper by the magnetic field, and the Hall coefficient is shown to exhibit hole features near the electron energy band top. The second system discussed here is composed of two parallel planar quantum wells separated by a potential barrier, which exhibits electron-hole Coulomb drag effects shown to involve nonlinearity.

By applying the technique of Z-contrast imaging to the study of a GaAs/AlGaAs multilayer using a newly developed 300kV scanning transmission electron microscope, we show that it is possible to directly observe the interlocking group III and group V sub-lattices on a column-by-column level. In addition to the direct observation of structural polarity in the [110] orientation, we show that, by using a maximum entropy approach to image processing, the experimentally acquired data can provide direct information on interface structures at atomic resolution.

This work addressed the MBE and EVTE growth of wide band gap semiconductor materials such as MnSe, Cd1-xMnxSe, and MnS1-xSex which have potential application for blue-green light emitters. It is the first time that EVTE was applied for high (Se, S, Cd) and low (Mn) vapor pressure materials, which required modification of the conventional design. The films were grown on GaAs 2° off (100) substrates and characterized using optical microscopy, SEM, EDS, X-ray, SIMS, Hall, and sheet resistance measurements. The deposition process parameters will be reviewed and related to results such as film composition, surface morphology, uniformity, and crystallinity. We report on growth of Cd1-xMnxSe with 0.42<X<0.99 and MnS1_xSex with 0.58<X<0.67. Different methods of controling elemental composition will be discussed. Grown materials show good surface morphlogy and uniformity. SIMS analysis demonstrated stable elemental composition throughout the film thickness and a sharp interface with the substrate.

The effect of growth interruption (GI) on the quality of interface between InGaAs quantum well (QW) and InP layer has been studied using transmission electron microscopy (TEM). The In1-xGaxAs (x=0.39) QW grown without GI has sharp and coherent interfaces. However, cellular structure instead of InGaAs QW was observed in the sample grown with 120 sec AsH3 purge during the first GI (before the growth of InGaAs QW). According to the composition analysis using energy dispersive X-ray (EDX), inside of cell is InP and boundary of cell is considered to be a mixture of In1-xGaxAs1-yPy and InAs1-xPx phases. Similar structure was observed in the sample grown with 30 sec AsH3 purge after 30 sec PH3 purge during the first GI. Our results indicate that long time AsH3 purge during the first GI is detrimental to the formation of InGaAs QW. For the sample grown with AsH3 purge less than 40 sec during the second GI (after the growth of InGaAs QW), InGaAs QW is formed with sharp and coherent interfaces. However, if the surface of InGaAs QW is exposed to AsH3 gas for long time (~ 120 sec), dislocations are generated at the interface bewteen InGaAs QW and InP cap layer.

We have studied the carrier concentration dependence of the magnetic-field-induced semimetal-to-semiconductor transition in AlxGai1-xSb/lnAs quantum wells for the magnetic fields up to 24T. The electron carrier concentration in InAs well was varied by the negative persistent photoconductivity effect. We found that electrons and holes coexisted in x = 0.1 and 0.2 samples. In the x = 0.2 sample, the semimetallic phase turned into the semiconducting phase when the holes vanished at 5T. This semimetal-to-semiconductor transition shifted to a higher field when the electron carrier concentration decreased. The results are consistent with the theoretical band structure.

Single crystal Mn thin films have been successfully grown on GaAs(001) substrates for the first time by molecular beam epitaxy. The bulk atomic structure of the manganese films is determined to be the face-centered-cubic metastable phase with the lattice parameter of 0.362 nm, by in situ reflection high energy electron diffraction (RHEED) and ex situ x-ray diffraction (XRD).

A self-aligned fabrication scheme of a novel AlGalnP/GalnAs/GaAs-MODFET device has been developed. Two characteristic features have been incorporated in the device structure: An AlGaInP barrier which provides a larger conduction band offset than the commonly used AlGaAs and a highly carbon-doped p-type GaAs gate structure which supports a very simple fabrication scheme. Using 1 μm optical lithography we have fabricated first demonstrator devices with a current gain cut-off frequency of 60 GHz and a power gain cut-off frequency of 140 GHz. In addition, the devices show large gate-drain diode breakdown voltages in excess of 30 V and gate currents as low as 50 nA even at gatesource voltages of -5 V.

A new sulfur passivation technique for GaAs surface by using S2Cl2 instead of (NH4)2Sx has been developed. Auger electron spectroscopy verifies the passivated surface is almost completely free of oxygen. The results of X-ray photoelectron spectroscopy indicate a relatively strong bonding between S and substrate atoms. A clean surface can be achieved by annealing in vacuum at 600°C. ZnSe thin films grown by hot wall epitaxy on S2Cl2 passivated GaAs show improved crystalline quality compared with those treated by conventional method, as indicated by Raman scattering measurements.

We report the growth of Zn1-xMnxSe films on GaAs(100) by hot wall epitaxy (HWE) up to a Mn concentration of 52%. The crystal structures of Zn1-xMnxSe layers were characterized by x-ray diffraction and Raman scattering. For the first time Zn1-xMnxSe(111) layers on GaAs(100) substrate have been grown and mixed phases of zinc-blende and hexagonal structure have been observed over the range 0.19≤x≤0.52.

a-GaN thin films have been grown on (0001) sapphire by a plasma-enhanced atomic layer epitaxy (PEALE) technique using a GaN buffer layer grown at lower temperatures. Both single crystal and polycrystal thin films have been obtained depending on the growth conditions, particularly, oxygen contamination of the plasma source and the substrate temperature. The orientation relationship between the single crystal film and the substrate is [0001]GaN//[0001]Al2O3, [l100]GaN//[1210]Al2O3 and [2110]GaN//[l100]Al2O3. The polycrystalline film has the c-axis perpendicular to the substrate and contains the same orientation found in the single crystal film. However, two additional orientations have been found that are rotated approximately ±19° from the single crystal orientation. The defect structures at the film/substrate interface were investigated by various X-ray methods such as rocking curves and phi scans, along with plane-view and cross sectional TEM. Possible growth mechanisms of both the single crystal and polycrystalline films will be discussed.

Cross-sectional Transmission Electron Microscopy (TEM) was used to probe dislocation density and crystallographic orientation relationships in epitaxial GaN layers grown on (0001) sapphire substrates. These Metallo-Organic Chemical Vapor Deposited (MOCVD) structures contained a 200 Å A1N buffer layer. Previous studies1 have incorporated 500 Å (or thicker) A1N buffer layers. It was found that thinner A1N buffer layers may be used without deterioration of GaN crystal quality. Threading dislocation density of ~108 #/cm2 was estimated from bright field micrographs. The relative crystallographic orientations of the substrate and epi-layers was determined by comparing real and simulated electron diffraction patterns. This revealed a 30° ‘twist’ between the basal plane of the sapphire substrate and the AlN/GaN epilayers. XTEM including High Resolution TEM (HRTEM) and HRTEM image simulations are presented.

A combined characterization of theoretical calculation and experimental measurements, including Raman scattering, photoluminescence and cross sectional transmission electron microscopy, has been made on GaAs-AlxGa1-xAs multiple quantum wells (MQW) structures with different well widths grown by metalorganic chemical vapor epitaxy (MOCVD) with a modified reactor. Various parameters of these MQWs are obtained. The results with and without the alkyl push flow are compared. Related physical phenomena are discussed.

The GaInP/AlGaInP heterostructure was grown on (100) GaAs substrate using low pressure metal-organic vapor phase epitaxy (LP MOVPE) . The growth temperature and pressure were held constant at 740 °C and 40 torr, respectively. The GalnP multiquantum well layers from 10 Å to 85 A were lattice matched to the substrate. High resolution transmission electron microscopy and low temperature photoluminescence measurements indicated that the GaInP/AlGaInP well layers were uniform in thickness and that the interface was abrupt and free of defects. For high performance of visible laser diodes, highly doped p-AlGaInP layer(8X1017/cm3) was obtained. It was also found that the Zn acceptor concentration increased with growth rate. In this study, the GaInP/AlGaInP laser diode, 645nm and 20mW, was fabricated by employing multiquantum well and highly doped p-cladding layer.