RESONANT TUNNELLING IN DOUBLE-BARRIER HETEROSTRUCTURES WITH AN ACCUMULATION LAYER

Two modes of electron gas injection in resonant tunnelling through GaAs/AlGaAs double-barrier heterostructures were revealed while studying their current-voltage characteristics. Examining peculiarities of the characteristics within the temperature range 4-350 K and under a high magnetic field, we were able to distinguish the contribution to resonant tunnelling of ballistic electrons mjected from a three-dimensional electron gas in the emitter contact and that of electrons injected from a two-dimensional electron gas in the accumulation layer formed near the emitter barrier.

Deep-level defects in n-type GaAsBi alloys grown by molecular beam epitaxy at low temperature and their influence on optical properties

Deep-level defects in n-type GaAs1-x Bi x having 0 ≤ x ≤ 0.023 grown on GaAs by molecular beam epitaxy at substrate temperature of 378 °C have been injvestigated by deep level transient spectroscopy. The optical properties of the layers have been studied by contactless electroreflectance and photoluminescence. We find that incorporating Bi suppresses the formation of GaAs-like electron traps, thus reducing the total trap concentration in dilute GaAsBi layers by over two orders of magnitude compared to GaAs grown under the same conditions. In order to distinguish between Bi- and host-related traps and to identify their possible origin, we used the GaAsBi band gap diagram to correlate their activation energies in samples with different Bi contents. This approach was recently successfully applied for the identification of electron traps in n-type GaAs1-x N x and assumes that the activation energy of electron traps decreases with the Bi (or N)-related downward shift of the conduction band. On the basis of this diagram and under the support of recent theoretical calculations, at least two Bi-related traps were revealed and associated with Bi pair defects, i.e. (VGa+BiGa)(-/2-) and (AsGa+BiGa)(0/1-). In the present work it is shown that these defects also influence the photoluminescence properties of GaAsBi alloys

Energy Levels and Electrical Activity of Dislocation Electron States in GaAs

Experimental results are presented confirming that the two energy levels in GaAs: E$\text{}_{c}$ - 0.68 eV and E$\text{}_{v}$ + 0.37 eV, discovered in plastically deformed crystals, belong actually to dislocations. In view of recent identification of the electron state of misfit dislocations at an InGaAs/GaAs interface, a correspondence between these levels and dislocation types has been reinterpreted. The first mentioned leve1 belongs likely to α while the second one to β dislocations of 60° (glide set) type. Such a correspondence is compatible with the observed effect of irradiation on dislocation glide motion in GaAs. It is also argued that these energy levels are involved in the phenomenon of unquenchability of the EL2 defects placed in high-stress regions near dislocations

Deep-Level Defects at Lattice-Mismatched GaAsSb/GaAs Interface

Lattice-mismatch-induced defects were studied by means of deep-level transient spectroscopy in high-purity GaAs$\text{}_{1-x}$Sb$\text{}_{x}$ layers (x = O to 3%) grown by liquid phase epitaxy on GaAs substrates. Microscopic nature and formation mechanism of two electron traps and two hole traps, which appeared in the layers as a result of Sb incorporation into the crystal lattice, are briefly discussed

Effect of Interface Roughness on Resonant Tunnelling in Double-Barrier Heterostructures

We argue that the well-boundary roughness in a double-barrier heterostructure induces subsidiary subbands in the quantum well which, in turn, lead to the appearance of a broad shoulder beyond the principal resonance peak in the current-voltage characteristics

Aharonov-Bohm Interference of Holes at Dislocations in Lattice-Mismatched Heterostructures

We have succeeded in revealing Ahaxonov-Bohm type interference of holes in macroscopic semiconductor sample containing an array of straight-line dislocations. This interference has been observed at helium temperatures as oscillations in the forward current flowing through p$^+$-n junction of the lattice-mismatched GaAs$_{1-x}$Sb$_x$/GaAs heterostructure while measured as a function of the magnetic field perpendicular to the current. The oscillation cycles arise when a primary hole wave meeting the Read's cylinder of a misfit dislocation interferes with a wave which circled completely round the cylinder

Electric Field Enhanced Emission of Holes from the Double Donor Level of the EL2 Defect in GaAs

Strong electric-field enhancement of the thermal emission rate of holes from the doubly ionized charge state of the EL2 defect was revealed with the deep-level transient spectroscopy in p-type GaAs and analyzed in a model of phonon-assisted tunnel effect. Similar dependence observed for the electric field directions parallel to three main crystallographic axes suggests tetrahedral symmetry of the defect which is consistent with its identification as the arsenic antisite

Native Defects in Gallium Arsenide Grown by Synthesis, Solute Diffusion Method

High-purity n-type GaAs crystal was grown by the Synthesis, Solute Diffusion (SSD) method. Deep Level Transient Spectroscopy (DLTS) characterization of the crystal revealed three deep traps related to native defects. Microscopic origin of the traps is discussed and prospective use of SSD-grown GaAs as a bulk material with the high luminescence efficiency is emphasized

Observation of the Coulomb Blockade at 77 K in a Lattice-Mismatched GaAs/Si Heterojunction

We investigated current-voltage characteristics of a lattice-mismatched GaAs(n)/Si(p) heterojunction. For low bias voltages at 77 K it exhibits a behaviour characteristic of the Coulomb blockade. We discuss why this unexpected phenomenon can occur in the investigated structures

Transformation of Native Defects in GaAs under Ultrasonic Treatment

Effect of high-intensity ultrasonic vibration on the spectrum of deep electron traps in bulk GaAs has been studied giving rise to a discussion on microscopic structure of native defects associated with the traps