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A description on a donor center embedded in a thin heterostructural barrier separating a semiconductor medium into two halves is presented. As a result of the small thickness of this barrier, the wave function of an electron bound by the donor center shifts almost completely into both halves of the surrounding semiconductor medium.

Research was conducted to examine the impact of heterointerfaces on the phonon assisted electron intersubband transition rates and optical phonon modes in step quantum well structures for intersubband lasers. Results showed that interface-phonon interactions provide larger transition rates up to an order of magnitude compared with transition rates calculated using bulk phonon modes and bulk Frohlich interaction Hamiltonian.

A two-dimensional Boltzmann transport survey of breakdown in pseudomorphic heterojunction field effect transistors (HFET's) reveals the impact ionization breakdown in these structures. It models the effects of the energy conservation equation and the space charge effects of generated carriers. The high field region in the vicinity of the gate corner and the channel near the top heterojunction influence the impact ionization breakdown. A thin pseudomorphic layer having a high threshold energy for impact ionization improves the breakdown voltage of the HFET's.

Analysis of a quantum well-based far infrared laser that employs optical pumping to incorporate population inversion in the laser reveals that a high pumping power density is essential to induce population inversion in the valence band structure with high intersubband scattering rates while a moderate pumping power density is sufficient in the conduction band structure. A maximum population inversion of 2.1 times 10 to the power of 11 sq cm is seen for conduction band structure at 2 kW/sq cm of pumping power density.

Single-drift GaAs TUNNETT diodes were mounted on diamond heat sinks for improved thermal resistance and evaluated around 100 GHz in a radial line full height waveguide cavity. The diodes were fabricated from MBE-grown material originally designed for diodes that operate in CW mode around 100 GHz on integral heat sinks. An RF output power of more than 70 mW with a corresponding dc to RF conversion efficiency of 4.9% was obtained at 105.4 GHz. This is the first successful demonstration of GaAs TUNNETT diodes mounted on diamond heat sinks. To the authors' knowledge, these dc to RF conversion efficiencies and RF power levels are the highest reported to date from TUNNETT diodes and exceed those of any single discrete device made of group III-V materials (GaAs, InP, etc.) at this frequency. Free-running TUNNETT diode oscillators exhibit clean spectra with an excellent phase noise of less than -94 dBc/Hz, measured at a frequency off-carrier of 500 kHz and an RF output power of 40 mW.

A measurement of I-V characteristics of GaAs/In(x)Al(1-x)as/GaAs pseudomorphic barriers as a function of temperature enables analysis of variation of electron transport through X valleys with built-in biaxial strain. Low values of tunneling mass and barrier height ensure smooth transport through transverse X valleys, as revealed by comparisons between theoretical and experimental shifts in band-edge. Addition of indium increases the overall conduction and implies the importance of intervalley scattering on the transport process.

Tau-X mixing effects in GaAs/AlAs/GaAs quantum well structures are explained by a self-consistent numerical model. The model is computationally steady and efficient, simple in conception and has flexibility in application to modelling of devices. Tau-X mixing effects in GaAs/AlAs/GaAs are derived by the model from calculated wave functions which yields current-voltage (I-V) characteristics of single and double barrier quantum wells.

Atheoretical model for the investigation of the capacitance-voltage and the current-voltage characteristics of quantum well varactors was presented. The model predicted results which were comparable to that obtained through experiments. In addition, the model proved to be useful in the design and optimization of quantum well varactors. Using the model, a triple-barrier, double-well varactor with superior capacitance ratio and small bias range was fabricated.

It has been possible to demonstrate the efficient inhomogeneous broadening of the intersubband THz transitions in quantum wells due to the non-screening roughness of heterointerfaces.

The conventional Gummel-Poon large-signal BJT model forms the basis for the development of an HSPICE heterojunction bipolar transistors (HBT) macro model for the characterization of InP-based single HBT's. The model explains the collector transit-time delay effects and the soft breakdown characteristics of the InAlAs/InGaAs single HBT's. The DC and small-signal microwave characteristics of the HBT's and integrated transimpedance amplifiers have been analyzed. The calculations obtained from the model agree with experimental results.

The stationary characteristics and high-frequency conductance of dual-gate field-effect transistors with inhomogeneous capacitive connection between gates and a current-conducting channel for an electron enhancement control mode are studied. The high-frequency gate currents have depended on the stationary channel current direction.

A model of very short-channel field-effect transistor (FET) controlled by a nonplanar prismoidal gate which efficiently depletes a thin electron channel in a very narrow strip around the gate apex, is presented and its stationary JV features are mentioned. It is observed that both the 'standard' regimes featuring quasisaturation of the drain current [j.sub.D], with a rise in the drain-source voltage [u.sub.DS], and nonstandard regimes, with reducing [j.sub.D][u.sub.DS] features exist in the selected FETs and a 'self-blocking' current [j.sub.D].

Electron wave tunneling through a rectangular heterostructural emitter barrier is considered in the case of a homogeneous high-frequency (HF) alternating electric field directed normal to the barrier interfaces. An effect can be used to optimize tunnel barrier emitters for ballistic transit-time tetrahertz-range oscillators.

The dependence of a small transmitted oscillating wave amplitude on the frequency omega and the value of V(sub 1)(x) is described. The dependence of the tunneling probability on all the parameters of the potential V(sub 1)(x) is considered in detail.

The interactions between ballistic (or quasiballistic) electrons accelerated by a dc electric field in an undoped transit space (T space) and a small ultra high frequency ac electric field are considered to calculate the linear admittance of the T space. The implementation of the considered tunnel injection transit time oscillator diode promises to lead to efficient and powerful sources of terahertz range radiation.

Real-space transfer (RST) of electrons or holes can occur naturally in each layered heterostructure as a result of a parallel current transport in the layers. The results of dispersion relation calculations for a structure, which include the QW layer L1 overgrown on the cleaved edge of the acceptor doped SL2 and covered by the barrier L3 are briefly stated.