Epitaxial metal-III-V semiconductor heterostructures

Stable and epitaxial metal III–V semiconductor heterostructures feature as the main topic in the series of Materials Science Reports Review Journal published by North Holland, Amsterdam. Written by a group of authors from Bellcore, Red Bank, NJ, USA, the report discusses metal semiconductor heterostructures (MSH) from their experience of MBE growth focussing special attention on the initial stages of growth of metal films on compound semiconductors.     

Electron tunnelling in semiconductor heterostructures

A theory of electron tunnelling in GaAsGa_1?xAl_xAsGaAs heterostructures is presented. The theory takes into account the different non-parabolic energy dispersion relations in the two materials. Calculated values of allowed energy levels are also presented for structures used in earlier experiments. Results of optical absorption experiments are found to agree with theory within 1 meV, but the results of double-barrier tunnelling experiments differ from theory by a factor of about 1.5.     

Photoreflectance characterization of semiconductors and semiconductor heterostructures

The electromodulation method of photoreflectance (PR) is becoming an important tool for the characterization of semiconductors, semiconductor interfaces and semiconductor microstructures such as superlattices, quantum wells, multiple quantum wells and heterojunctions. Since PR is contactless, requires no special mounting of the sample and can be performed in a variety of transparent ambients it can be utilized for in-situ monitoring of growth at elevated temperatures, in-situ elevation at 300K before the samples are removed from the growth/processing chamber as well as convenient ex-situ characterization. This invited article discusses some recent uses of PR to measure (a) the direct gap (and spin-orbit split component) of InP up to 600° C, (b) strains in Si at the Si/SiO₂ interface, (c) changes in the surface Fermi level of GaAs caused by photowashing, (d) quantized intersubband transitions in a GaAs/Gao_0.82Al_0.18As multiple quantum well and (e) two-dimensional electron gas effects in selectively dopedn-Ga_o.7Al_o.3As/ GaAs heterostructures.     

Tunneling time asymmetry in semiconductor heterostructures

Analytical expressions are given for the difference between left-to-right and right-to-left tunneling times in asymmetric single- and multiple-barrier heterostructures. This tunneling time asymmetry is related to the phase difference of the reflection coefficients of the electron wavefunction for the two tunneling directions. Examples for single- and double-barrier heterostructures are given. The treatment in this paper can be used for designing devices with asymmetric frequency characteristics with respect to the electron tunneling direction     

Mechanism of dicke superradiance in semiconductor heterostructures

Dicke superradiance is regarded as an intermediate phase in the transition from spontaneous to stimulated emission in semiconductor laser heterostructures. A phenomenological model that describes the formation of superradiant domains (“macrodipoles”) in the active region of heterostructures is suggested. It is shown that the characteristic emission time of these domains falls within the subpicosecond range.     

Defects and defect reduction processing in semiconductor heterostructures

Defects such as dislocations and interfaces play a crucial role in the performance of heterostructure devices. The full potential of GaAs on Si heterostructures can only be realized by controlling the defect density. The nature of misfit dislocations at the heterointerface has been studied and a mechanism for the formation of 60° and 90° misfit dislocations has been proposed. Threading dislocations in the epilayer are the most prominent defects and their density has to be controlled to fully utilize the properties of semiconductor heterostructures. Various processes to reduce defect densities in the epilayers have been discussed and in particular, the use of strained layer superlattices to reduce the threading dislocation density has been presented in this paper. Several superlattice structures have been used to reduce the density of threading dislocations in the GaAs epilayer. In this study, we have optimized the use of strained layer superlattices with respect to the position, period and number to reduce and control the dislocation density. The use of strained layer superlattices in conjunction with rapid thermal annealing was found to be the most effective method in reducing threading dislocation density. Transmission electron microscopy has been used to study the dislocation density reduction and the interaction of threading dislocations with the strained layers.     

Silicon-based semiconductor heterostructures: column IV bandgapengineering

The use of strained layer epitaxy to grow high-quality Ge_x Si_1-x/Si heterostructures and their application to a wide range of heterostructure devices are addressed. The author reviews the mechanisms of strained layer growth, the bandstructure of the resulting material, and its use in test devices, including superlattice avalanche photodiodes for fiber optic communication, intrasubband optical detectors and arrays operating in the 10-15 μm wavelength range, mobility enhanced modulation-doped transistors, heterojunction bipolar transistors with cutoff frequencies of 75 GHz, and negative resistance devices based on resonant tunneling and real-space carrier transfer     

Realistic semiconductor heterostructures design using inverse scattering

We discuss the construction of optimized electronic filters using inverse scattering methods. We study a wide range of densities and temperatures, room temperature included. Discretization methods of the potential (including the self-consistent potential of the conduction electrons) are worked out that retain all its properties.     

The future of power semiconductor device technology

Power electronic systems have benefited greatly during the past ten years from the revolutionary advances that have occurred in power discrete devices. The introduction of power metal-oxide-semiconductor field-effect transistors (MOSFETs) in the 1970s and the insulated gate bipolar transistors (IGBTs) in the 1980s enabled design of very compact high-efficiency systems due to the greatly enhanced power gain resulting from the high input impedance of these structures. Recently, significant improvements in the performance of silicon-power MOSFETs has been achieved by using innovative vertical structures with charge coupled regions. Meanwhile, silicon IGBTs continue to dominate the medium- and high-voltage application space sue to scaling of their voltage ratings and refinements to their gate structure achieved by using very large scale integration (VLSI) technology and trench gate regions. Research on a variety of MOS-gated thyristors has also been conducted, resulting in some promising improvements in the tradeoff between on-state power loss, switching power loss, and the safe-operating-area. Concurrent improvements in power rectifiers have been achieved at low-voltage ratings using Schottky rectifier structures containing trenches and at high-voltage ratings using structures that combine junction and Schottky barrier contacts. On the longer term, silicon carbide Schottky rectifiers and power MOSFETs offer at least another tenfold improvement in performance. Although the projected performance enhancements have been experimentally demonstrated, the defect density and cost of the starting material are determining the pace of commercialization of this technology at present     

Piezoelectric effects in semiconductor heterostructures: applications and consequences

The piezoelectric (PZ) effect in strained semiconductor heterostructures can be used as an additional degree of freedom in designing novel heterostructures with desired optoelectronic properties. After a short review of previous work in the field, we discuss two examples in which the presence of the PZ field is either beneficial or unwelcome. First, we present a wavelength-tunable laser diode whose tuning mechanism is based on the quantum confined Stark effect and we show that the tuning range of the device can be significantly enhanced if the active quantum well contains a PZ field. Next, we discuss the case of nitride heterostructures where unwanted polarization-induced electric fields limit seriously their performance in optoelectronic applications. We show that the use of quaternary nitrides can help circumvent this problem.     

世界半导体业发展图说

半导体产业结构的演变1、1986年前——半导体产品主要由集成器件制造商(IDM-Integrated Device Manufacturer)生产。系统/集成电路设计、工厂(生产线-Fab)和组装测试(Assembly&Test)三业分工。     

The global route to future semiconductor technology

The idea of constructing a technology roadmap for semiconductors was generated in the early 1990s by the need to bring some consistency among programs proposed in the United States in the field of semiconductors by academic institutions, national laboratories, and commercial semiconductor manufacturers (industry). In this paper the author presents an overview of the 2001 International Technology Roadmap for Semiconductors (ITRS). The 2001 ITRS is the result of more than 800 researchers from the five leading regions in the semiconductor industry. In this document it is reported that the pace of scaling continues on a two-year cycle up to the present 130-nm technology node. It is anticipated that technology node introduction will resume on a three-year cycle with the next (90 nm) technology node, but so it was predicted several times before and then readjusted to a two-year introduction for the next technology node. Also a new chapter looking beyond classical CMOS has been introduced     

Efficient electro-optic semiconductor medium based on type-II heterostructures

An electro-optic medium based on the type-II semiconductor superlattice is proposed. Electrooptic modulation of the intensity of optical reflectance of the electro-optic medium integrated into a vertical Fabry-Perot cavity is studied by the optical-reflectance-spectroscopy method. The experimental data are approximated using an oscillator model of exciton absorption. The efficiency of the electro-optic medium in the case of detuning from the absorption peak by 50 meV in electric fields of 0–50 kV/cm is 10^?9 m/V at a medium filling factor of 100%.     

Type-I semiconductor heterostructures with an indirect-gap conduction band

In spite of a great number of publications concerned with studies of semiconductor heterostructures, the type-I semiconductor heterostructures, in which the ground electron state belongs to the indirect-gap (X and L) minimums of the conduction band, have remained poorly understood until recently. In this paper, the possibility is discussed of using III–V semiconductor compounds to create type-I semiconductor heterostructures with electron states belonging to the indirect-gap minimums of the conduction band.     

Photosensitivity of heterostructures based on finely ground semiconductor phases

A new type of heterostructure is suggested and developed. The heterostructures are based on the direct contact of a bulk semiconductor with a dielectric layer in which a finely ground semiconductor phase is dispersed. In Si-and GaAs-based heterostructures of this type, rectification and photovoltaic effects are observed. It is shown that illumination of such structures so that the side of the dielectric layer with the built-in finely ground semiconductor phase is exposed to light induces a broadband photovoltaic effect deep within the fundamental absorption band of the bulk semiconductor.     

On the band-structure lineup at Schottky contacts and semiconductor heterostructures

The band-structure lineup at semiconductor interfaces is explained by the intrinsic interface-induced gap states (IFIGS) that derive from the complex band structures of the semiconductors. The barrier heights of metal–semiconductor or Schottky contacts as well as the band-edge offsets of semiconductor heterostructures are composed of a zero-charge-transfer term plus an electrostatic-dipole contribution which are determined by the IFIGS branch-point energies of the semiconductors and the electronegativity difference of the two materials in contact, respectively. This concept will be illustrated by experimental core-level shifts induced by metal adatoms on group-IV semiconductor surfaces. Choosing Si and SiO₂ Schottky contacts and heterostructures as typical examples, it will be demonstrated that the IFIGS-and-electronegativity concept self-consistently explains the barrier heights of Schottky contacts and the valence-band offsets of heterostructures. The IFIGS-and-electronegativity concept also resolves the alleviation of the Fermi-level pinning by ultra-thin insulator interlayers in Schottky contacts. Finally, the modification of Schottky barriers by atomic interlayers will be discussed.     

Multi-wavelength integrated optical-laser emission modulator based on semiconductor heterostructures

Small-signal-controlled optical modulator structure capable of operation at several wavelengths is suggested. It is shown that the application of spectrally selective mirrors makes it possible to develop optically integrated cavities that provide lasing at prescribed discrete wavelengths and a control section that can vary the internal optical loss. The main relationships between the lasing-mode switching conditions and optical-modulator structure parameters are determined. Optical modulators for the 1060–1080 nm spectral range, with a distributed Bragg reflector as one of the mirrors, are developed and experimentally investigated. It is shown that small-signal control by a forward current can switch the lasing between optically integrated Fabry-Perot cavities at a 5–20 ns rate.