The heterointerfaces of single quantum wells (SQWs) and the characteristics of SQW lasers on Si substrates grown with Al0.5 Ga0 5As/Al0.55Ga0.45P intermediate layers (AlGaAs/AlGaP ILs) entirely by MOCVD are reported. The surface morphology and the heterointerfaces of SQWs grown on Si substrates with the AlGaAs/AlGaP ILs are smoother than those of the two-step-grown sample. The two-dimensional growth of the AlGaAs/AlGaP ILs on a Si substrate contributes to obtain the smooth heterointerface. The excellent lasing characteristics are obtained by the AlGaAs/AlGaP ILs, which are caused by the smooth heterointerfaces. The lasers grown with the AlGaAs/AlGaP ILs show the averaged threshold current density of 1.83 kA/cm2 and the averaged differential quantum efficiency of 51.9 % under cw condition at room temperature.

Monolithic colliding pulse mode-locked (CPM) multiple quantum well lasers generating optical pulses as short as 600 femtoseconds are reported. The CPM laser is built on a single chip of InGaAs/InGaAsP multiple quantum well laser. The pulse repetition rates are synchronized with an rf synthesizer up to 40 GHz in hybrid mode-locking scheme. In passive mode-locking scheme, a record high repetition rate of 350 GHz has been achieved. All the sub-picosecond pulses obtained have pulse shapes of sech2 and transform-limited timebandwidth products between 0.30 to 0.34. This new optical source is very useful for ultra-high speed optical switching and optical logic in optical fibers, and ultra-long distance optical soliton transmissions.

GaAs single quantum well lasers have been successfully grown at low temperatures by a modulated beam epitaxy process in which the Al/Ga flux is held constant while the As flux is periodically shut off to produce a metal-rich surface. Devices grown at a substrate temperature of 500 °C exhibit threshold current densities below 1 kA/cm2. This value is lower than normally grown low temperature lasers and is the lowest achieved by any low substrate temperature growth technique. In addition, low temperature (10 K) photoluminescence of single quantum wells grown with this technique exhibit full-width half maximum values, comparable to that attainable by higher temperature growth techniques. The improved quality of these low temperature grown quantum structures is attributed to both a smoothing of the growth front and a reduction of excess As during the modulated beam epitaxy process. The high growth rates and less frequent shutter operation of this technique make it a more practical than migration enhanced epitaxy or atomic layer epitaxy for low temperature growth.

We report the realization of high quality strained InGaAs/GaAs multiple quantum wells (MQW) grown on planar GaAs (100) substrates through optimization of molecular beam epitaxical (MBE) growth conditions and structure. Such MQWs containing ∼ 11% In have lead to the realization of an asymmetric Fabry-Perot (ASFP) reflection modulator with a room temperature contrast ratio of 66:1 and an on-state reflectivity of 30%. For In composition ≥ 0.2, the improved optical quality for very thick (gt;2μm) InGaAs/GaAs MQWs grown on pre-patterned substrates is demonstrated via transmission electron microscopy (TEM) and micro-absorption measurements.

We report the realization of (a) an optically bistable switch using a strained resonant tunneling diode (RTD) and (b) highly strained RTDs exhibiting simultaneously high peak current densities (Jp) and peak-to-valley current ratios (PVR) suitable for high-speed electronic switching. Both of these make use of RTDs with (InAs)M/(GaAs)N strained short period multiple quantum well regions with AlAs barriers in a triple-well, double barrier structure. For the former, high contrast ratio (20:1) and an on state reflectivity of 46.5 % has been obtained at room temperature in an optically bistable switch involving a strained InGaAs/GaAs (100) multiple quantum well based asymmetric Fabty-Perot reflection modulator, detector, and a strained RTD and a Si field effect transistor. For the latter, we have obtained a Jp of 125 kA/cm2 with a PVR of 4.7 at room temperature.

AlGaAs/GaAs double-heterostructure (DH) optical waveguides on Si substrates which is important in future opto-electric integrated circuits (OEICs) utilizing both Si and GaAs devices is analyzed by the effective index method and fabricated by metalorganic chemical vapor deposition (MOCVD).

The structures contain 0.8-μm-thick GaAs guiding layer sandwiched between two 1-μm-thick Al0.1Ga0.9 As cladding layers. All the layers were grown by MOCVD on (100) 2°-off Si substrates by two step method. A top cladding layer was etched leaving 2-μm wide mesa-stripes. The etched depth was changed from 0.65 to 0.90 μm. The field profiles were calculated and measured for 1.3 μm wavelength light. The measured and calculated profiles agree quite well with each other for all the. waveguides having different mesa height. This agreement makes us possible to design more complicated AlGaAs/GaAs waveguides and modulators on Si substrates.

In(As, P)/InP strained multiple quantum wells (SMQW's) were grown with gas-source molecular-beam epitaxy (GSMBE). A successful control of the As composition was achieved over a wide range by using two techniques. High-quality samples were characterized structurally and optically by x-ray diffractometry, transmission electron microscopy (TEM), photoluminescence (PL) and absorption measurements. Excitonic emission energy and the critical layer thickness of In(As, P)/InP SMQW's are calculated as a function of the As composition. The results show that 1.06, 1.3 and 1.55 μm excitonic emission can be achieved at room temperature using this material system. We also discuss the perspective of using In(As, P)/InP SMQW's for modulator application.

In this paper, we have studied the photoemission from quantum wells (QWs), quantum well wires (QWWs) and quantum dots (QDs) of degenerate Kane-type semiconductors, on the basis of a newly derived electron dispersion law considering all types of anisotropies within the framework of k.p formalism. It is found, taking n-Cd3 As2 as an example, that the photoemission increases with increasing photon energy in a ladder-like manner and also exhibits oscillatory dependences with changing electron concentration and with film thickness, for all types of quantum confinement. The photoemission current density is greatest in QDs and least in QWWs. In addition, the theoretical results are in agreement with the experimental observation as reported elsewhere.

We investigated the conduction mechanism and performance of GaAs-A1GaAs quantum-well infrared photodetectors and proposed a conduction model consisting of Poole-Frenkel-like emission from wells and carrier relaxation wells. The model agrees with the measured photocurrent and dark current. The detector's noise current is given by a simple shot noise formula. Analysis has shown that the photocurrent and the noise current are inversely proportional to the barrier width, while the dark current is inversely proportional to the square of the barrier width.

Advances in epitaxial growth techniques such as molecular beam epitaxy and metal organic chemical vapor deposition have facilitated the formation of high quality III-V heterostructures with dimensional control down to atomic levels, with abrupt doping and near-defect-free interfaces. The flexibility and remarkable control offered by these techniques have resulted in the fabrication of new devices based on confinement or modulation of carriers in thin III-V heterostructures. Quantum wells and superlattice based devices are expected to be utilized in optical information processing as sources, modulators, and detectors. In this paper, we will review the general epitaxial requirements for quantum wells and superlattices based devices, and discuss the fabrication and properties of a new class of infrared photodetectors that employ intraband transitions in quantum wells.

A 3-dimensional phase diagram is introduced to describe the dependence of the RHEED pattern from GaAs(111)B surface on growth conditions. The 2×2, transitional(1×1), and √19×,√19 surface reconstructions correspond to different zones in the phase diagram. A equation is given for the planes that separate these zones, which fit experimental data well. Homoepitaxial films on GaAs(111)B grown in the 2×2 region generally have bad crystal quality as determined by the ion channeling, and growth in the √19×√19 region generally yields rough surface morphology. At higher substrate temperatures (∼ 650 °C), featureless films with minimum ion channeling yields of less than 4% are achieved.

The optical bowing behavior of polycrystalline thin film Culn1-yGaySe2 alloys is dependent upon the Cu stoichiometry. The variation in optical band gap, Eg, for alloys in which Cu is near stoichiometric (25 at.%) is parabolic and follows the relationship: Eg(y) = 1.011 + 0.421 y + 0.244 y2 (eV), where y is the alloy parameter, [at.% Ga] / [at.%Ga + at.%In]. Contrary to this, films with Cu-poor stoichiometries (∼19 at.% Cu) exhibit little alloy bowing: Eg(y) = 1.01 + 0.733 y - 0.046 y2 (eV). The increase in Eg with Cu deficiency appears to be the result of both a structural effect associated with tetragonal lattice shrinkage, ΔV = Vstoichiometric - VCu-poor (resulting from the presence of Cu vacancies) and a chemical effect, possibly associated with a counterbalance between p-d repulsion and anion displacement effects.

Boron nitride films were deposited by rf reactive sputtering. The composition of the film was determined by X-ray photo-electron spectroscopy(XPS). Optical properties of boron nitride were studied by IR spectroscopy. Resultant films showed optical characteristics similar to those of hexagonal boron nitride. The ratio of boron to nitrogen was varied from 3.11 to 1.45 by varying the amount of nitrogen. Resulting films have refractive index in the range of 2.05 – 3.21.

In recent years, a two-step electric field assisted diffusion or ion-exchange technique has been extensively studied for producing buried concentration profiles in glass [1,2,3], polymer [4,5], electrooptic and semiconducting [6,7] substrate materials to fabricate buried optical waveguide devices. The technique contains two separate diffusion processes and is quite complicated, cost and time consuming. In addition, theoretical analysis of the technique is too complicated to be used for calculating and tailoring concentration profiles. Many efforts have been made to pursue a one-step process for producing buried profiles. Very recently, a novel one-step technique [8] involving electric field assisted diffusion of silver ions into glass from molten AgNO3 bath with decaying silver concentration has been developed to produce buried Ag+ concentration profiles in glass substrate. The new technique is, from the practical operation point of view, relatively simple and is a significant improvement over the conventional two-step process.

Microcrystalline films of B-Si-Ge alloy have been deposited by the sputtering of Ge target in atmosphere of SiH4 and B2H6. Microcrystalline B-Si-Ge alloy/Si hetero-junction was fabricated on p-type Si(100) wafers with the resistivity of 1∼10 Ωcm. The barrier height of this Schottky structure was estimated to be in the range of 0.20∼0.30 eV which can be controlled by inclusion amounts of boron. The reverse biased Schottky characteristic using the microcrystalline B-Si-Ge alloy as to the gate shows the avalanche breakdown by illuminating of 6 μm light.

A short wavelength laser offers unique opportunities in high density optical recording as well as in laser printing. To achieve a compact blue laser, the current effort worldwide is primarily concentrated on achieving well-conducting p-type ZnSe and fabricating quantum well heterostructures so as to achieve a low threshold laser at room temperature. The recent milestone ‘an injection blue laser below room temperature’ gives us confidence that indeed we are on the right path. In photopumped lasers in various II-VI heterostructures, thresholds at room temperature comparable to the theoretical limit have been reported. This not only reinforces that indeed a room temperature injection laser is possible but when combined with earlier electron-beam pumped laser results, a scanned compact laser is also feasible.

In recent years several breakthroughs have demonstrated that an infrared emitting GaAs laser can be used to generate blue light through efficient second harmonic generation (SHG) in certain non-linear optical materials. Recent exciting results on SHG of GaAs lasers in KTP grating waveguides resulted in a blue laser with output power in the range of several milliwatts. Alternative schemes such as upconversion lasers and SHG in III-V quantum wells structures are presented.

In summary, various efforts to achieve compact blue lasers and their availability in the near future are presented.

Superlattices and quantum wells of Znl-xCdxSe/ZnSe, and heterostructures based on ZnSe/CdSe digital alloys have been grown by molecular beam epitaxy (MBE). Their optical properties were studied with particular emphasis on excitonic absorption and photopumped stimulated emission. Excitonic absorption is easily observable up to 400 K, and is characterized by extremely large absorption coefficients (α = 2×105cm−1). Optically pumped lasing action is obtained at room temperature with a typical threshold intensity of 100 kW/cm2. The lasing mechanism in these II-VI quantum wells appears to be quite different from that in the better studied III-V materials: in our case, the onset of stimulated emission occurs before the saturation of the excitonic absorption, and the stimulated emission occurs at an energy lower than that of the excitonic absorption.

We have succeeded in the growth of p-type ZnSe homoepitaxial layers. The layers have been grown by molecular beam epitaxy (MBE) on (100) ZnSe substrates dry-etched with BCI3 plasma to eliminate polishing damage. Nitrogen acceptors were incorporated by nitrogen radical doping during MBE growth. Hall measurement by using Pt electrodes have indicated that the N-doped ZnSe homoepitaxial layers are p-type with typical hole concentration of 8.9×1015 cm−3. 12-K photoluminescence (PL) from the layers exhibited strong neutral-acceptor-bound exciton emission (11) at 2.7931 eV, indicating the peak energy of 11 emission from the strain-free ZnSe:N.

The results of the x-ray spectral investigations of CdxHg1-xTe/GaAs thin films conducted with the help of “Camebax - microbeam” electron microprobe are presented. It is shown that the sensitivity of the microprobe combined with the mathematical processing based on the chemometric approaches Is sufficient to reveal the effects of the chemical bond on x-ray spectra.

Wide gap II-VI compound semiconductors are difficult to be doped amphoterically. After more than thirty years of research in II-VI compound semiconductors, there does not even exist a satisfatory simultaneous explanation as to why ZnSe can be easily doped n-type while undoped ZnTe only exhibits p-type conductivity. In this paper we propose an explanation based on the III-V/II-VI analogy which for the first time can explain these phenomena, and provide solutions to the problem of doping II-VI compound semiconductors.