The existence of type-II structures made from the combination of Ga_{1-x}AI_{x}As alloy and a short period GaAs/AlAs type-I superlattice is presented. Such three material structures are of type-II having at the same time electrons and holes of Γ-symmetry. This contrasts with the usual situation in type-II two material GaAs/AlAs structure where the ground state of electrons is of X-symmetry. The mechanism allowing creation of three material type-II structures is based on the difference of effective masses of electrons and holes. It should be valid for all similar semiconductor systems. Experimental results of photoluminescence and photoluminescence excitation studies of such structures made by Molecular Beam Epitaxy are presented. We determine the mutual positions of the electron and hole ground levels in the alloy and pseudoalloy and confirm that the studied structure is of type-II.
The application of pulsed lasers for vaporization (ablation) of solid targets appears to be the most natural way to produce high purity fluxes of atoms/ions suitable for epitaxial growth of thin films. Since the early 1960's this unique approach has been the subject of steadily growing interest in the deposition of metals, dielectrics, semiconductors and since 1987, high-T_{c} superconductors. Laser induced target surface morphology changes, properties of laser induced vapours and pulsed deposition rate associated with the use of a pulsed laser for vacuum epitaxy are discussed. A pulsed laser evaporation and epitaxy (PLEE) system is described and the results of PLEE application for the growth of Cd_{1-x}Mn_{x}Te and CdTe-Cd_{1-x}Mn_{x}Te quantum well and superlattice structures are reviewed. Feasibility of PLEE in bandgap engineering is also discussed.
We review recent magneto-optical investigations performed on HgTe-CdTe semimetallic superlattices. Far infrared magnetotransmission data obtained as a function of temperature, photon energy, and sense of circular polarization are compared with the predictions of a comprehensive new theory which fully incorporates the complexities of type-III superlattice band structure. It is found that the theory accounts for nearly all of the many unusual features which have been observed experimentally. These include the occurrence of two cyclotron resonances due to holes; the coexistence of electron and hole cyclotron resonances in the low temperature limit; the observation of three distinct CRA minima; a step-like change in the temperature dependence of the electron cyclotron mass; and a dramatic increase of the CRI absorption peak intensity with increasing magnetic field.
The nonequilibrium growth technique of molecular beam epitaxy (MBE) has provided for the fabrication and investigation of a multitude of novel layered heterostructures based on II-VI compound semiconductors. The ability to grow epitaxial metastable magnetic and semimagnetic semiconductors layered with conventional II-VI semiconductors has resulted in structures which, for example, exhibit frustrated antiferromagnetism, and a wide wavelength tunability due to selftrapping of excitons in ZnTe-containing layered structures and due to extremely large (≈ 1 eV) quantum shifts of light emission from MnTe/CdTe superlattice structures. In addition, the control in the stoichiometry of surfaces and the composition of molecular beams used in the MBE growth technique has allowed for the fabrication of very advanced heterostructures which have combined the II-VI and III-V families of compound semiconductors. The work which will be described in the following review represents a very small sampling of the many important results achieved in the field of II-VI based heterostructures. The topics have been selected to illustrate and provide an example of the utility of MBE and the potential of "engineered" II-VI heterostructures and quantum wells.
In this work interdiffusion and strain relaxation in In_{0.2}Ga_{0.8}As/GaAs single quantum wells subjected to rapid thermal annealing have been studied using photoluminescence and Rutherford backscattering of 1.5 MeV He^{+} ions. It has been found that the diffusion coefficient of In atoms in GaAs, evaluated from the photoluminescence spectra for the assumed Gaussian well shapes, agrees within 30% with that obtained using Rutherford backscattering. Channeling angular scans, through the ⟨110⟩ axial direction of the heterostructures indicate that strain relaxation in the intermixed wells is exclusively due to compositional shallowing of the wells.
We describe the main problems encountered in MBE growth of GaAs/AlAs superlattices and heterostructures. Then, basic features for the understanding of their electronic properties are given, in the envelope-function formalism, and some related optical experiments are reviewed.
Intersubband plasma excitation spectrum of lateral multiwire superlattices is investigated theoretically within the random-phase approximation. We examine the role of an interwire electron-electron interaction in regard to the depolarization shift.
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