The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications

D X centers, deep levels associated with donors in III‐V semiconductors, have been extensively studied, not only because of their peculiar and interesting properties, but also because an understanding of the physics of these deep levels is necessary in order to determine the usefulness of III‐V semiconductors for heterojunction device structures. Much progress has been made in our understanding of the electrical and optical characteristics of D X centers as well as their effects on the behavior of various device structures through systematic studies in alloys of various composition and with applied hydrostatic pressure. It is now generally believed that the D X level is a state of the isolated substitutional donor atom. The variation of the transport properties and capture and emission kinetics of the D X level with the conduction‐band structure is now well understood. It has been found that the properties of the deep level when it is resonant with the conduction band, and is thus a metastable state, are similar to its characteristics when it is the stable state of the donor. And it has been consistently found that there is a large energy difference between the optical and thermal ionization energies, implying that this deep state is strongly coupled to the crystal lattice. The shifts in the emission kinetics due to the variation in the local environment of the donor atom suggest that the lattice relaxation involves the motion of an atom (the donor or a neighboring atom) from the group‐III lattice site toward the interstitial site. Total energy calculations show that such a configuration is stable provided that the donor traps two electrons, i.e., has negative U. Verification of the charge state of the occupied D X level is needed as well as direct evidence for its microscopic structure.

Deep donor levels (DX centers) in III‐V semiconductors

A nitride semiconductor device including a light emitting device comprises a n-type region of one or more nitride semiconductor layers having n-type conductivity, a p-type region of one or more nitride semiconductor layers having p-type conductivity and an active layer between the n-type region and the p-type region. In such devices, there is provided with a super lattice layer comprising first layers and second layers which are nitride semiconductors having a different composition respectively. The super lattice structure makes working current and voltage of the device lowered, resulting in realization of more efficient devices.

Nitride semiconductor device

A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct ...

Photoluminescence of AlxGa1−xAs alloys

The high electron mobility transistor's (HEMT's) noise behavior is presented from theoretical and experimental points of view. The general method used in the high-frequency noise analysis is described and the different approximations commonly used in the derivation of the noise parameter expressions are discussed. A comparison between the noise performance of both MESFETs and HEMTs is carried out. The measurement techniques providing the noise figure and the other noise parameters are then described and compared. >

Noise modeling and measurement techniques (HEMTs)

Alloy broadening in photoluminescence spectra of Al x Ga 1-x As

A field-effect transistor (FET) using a two-dimensional electron gas (2DEG) as an electron channel is fabricated from GaAs grown by molecular-beam epitaxy. The doping profile of the field-effect transistor is described by the Dirac delta (δ) function. The subband structure of δ-doped GaAs is calculated. The characteristics of the δFET are a high concentration of the 2DEG, a high breakdown voltage of the Schottky contact, a narrow distance of the 2DEG from the gate, and a high transconductance. These properties are analyzed. Preliminary results for the extrinsic transconductance and for the transit frequency are obtained from δFET's having nonoptimized structures.

The delta-doped field-effect transistor (&#948;FET)

Temperature-dependent Hall-effect measurements are reported and analyzed in detail for $n$-type ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ of composition $0\ensuremath{\le}x\ensuremath{\le}0.40$ grown by molecular-beam epitaxy and highly doped with Si (${N}_{\mathrm{Si}}\ensuremath{\ge}5\ifmmode\times\else\texttimes\fi{}{10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$). A quantitative analysis using Fermi-Dirac statistics reveals for the composition range $0.20\ensuremath{\le}x\ensuremath{\le}0.40$ the presence of a hydrogenlike shallow Si donor which interacts with the $\ensuremath{\Gamma}$ valley and a deep Si donor related to the $X$ valley. In contrast to previous results, the thermal activation energy of the deep donor, determined to be ${E}_{\mathrm{dd}}=140\ifmmode\pm\else\textpm\fi{}10$ meV, does not change significantly with alloy composition. Only the ratio of shallow-to deep-donor concentration depends on composition. For $x\ensuremath{\le}0.20$, neither deep-donor nor persistent photoconductivity exists in $n$-type ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{A}\mathrm{s}:\mathrm{S}\mathrm{i}$. For $0.20\ensuremath{\le}x\ensuremath{\le}0.40$, however, the deep-donor concentration increases with $x$ while simultaneously the shallow-donor concentration decreases. The proposed interaction of the deep donor with the $X$ valley helps in understanding the persistent photoconductivity found in $n$-type ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ with $0.20\ensuremath{\le}x\ensuremath{\le}0.40$.

Shallow and deep donors in direct-gap n -type Al x Ga 1 − x A s : S i grown by molecular-beam epitaxy

A semiconductor device consisting of epitaxial material is provided with at least one monoatomic layer of doping atoms, i.e. with a layer which is just one atom thick. A particularly preferred device is a field effect transistor in which case the Dirac-delta doped layer 13 extends between the source and drain zones (18, 19) respectively. The field effect transistor can be constructed either with a homogeneous structure or with a hetero structure or with a superlattice structure. The field effect transistors described herein have a high transconductance and are capable of operating at high current densities.

Semiconductor devices with at least one monoatomic layer of doping atoms

A new sawtooth-shaped conduction- and valence-band potential in GaAs is generated by alternating n- and p-type Dirac-\ensuremath{\delta} doping, i.e., by interrupting growth of the GaAs host material but continuing doping. Photoluminescence measurements on this new superlattice at 2 and 77 K reveal high-intensity emission at energies below the band gap of the GaAs host material. The luminescence energy does not depend on the excitation density over five orders of magnitude. This result indicates short minority-carrier lifetimes even at low-density excitation and a stable low-energy band gap of the superlattice. The spontaneous carrier lifetime determined from high-intensity excitation amounts to 3.3 ns, which is comparable to bulk-type GaAs. The material design parameters for the new superlattice are established taking into account quantized electron and hole states in the V-shaped potential wells.

E. F. Schubert

Papers

Alloy broadening in photoluminescence spectra of Al x Ga 1-x As

The delta-doped field-effect transistor (δFET)

Shallow and deep donors in direct-gap n -type Al x Ga 1 − x A s : S i grown by molecular-beam epitaxy

Semiconductor devices with at least one monoatomic layer of doping atoms

Radiative electron-hole recombination in a new sawtooth semiconductor superlattice grown by molecular-beam epitaxy

E. F. Schubert

Papers

Alloy broadening in photoluminescence spectra of Al x Ga 1-x As

The delta-doped field-effect transistor (&#948;FET)

Shallow and deep donors in direct-gap n -type Al x Ga 1 − x A s : S i grown by molecular-beam epitaxy

Semiconductor devices with at least one monoatomic layer of doping atoms

Radiative electron-hole recombination in a new sawtooth semiconductor superlattice grown by molecular-beam epitaxy

The delta-doped field-effect transistor (δFET)