R. Eppenga

Possibility of green light emission from GaP/AlP (001) superlattices

Abstract Using ab initio band structure calculations based on the augmented spherical wave method and calculations of oscillator strengths based thereon, it is shown that monolayer type GaP/AlP (001) superlattices, in comparison to the earlier studied GaP and GaP: N materials, may show prospects for light emission in the green.

Low-frequency noise of quantum point contacts in the ballistic and quantum Hall regime

Abstract The low-frequency resistance noise of quantum point contacts is shown to be dominated by fluctuations in the electrostatic potential. Both in the ballistic and in the quantum Hall regime, the noise is strongly suppressed if the conductance is quantized. The suppression is enhanced by a strong magnetic field due to the absence of backscattering in the point contact. Additional minima are found in the noise as a function of the conductance due to the lifting of the spin degeneracy by the field.

Ab-initio determinations of semiconductor spin-orbit splittings from ASW

Abstract We demonstrate that the spin-orbit splittings of the valence and conduction bands at the Γ, L and X symmetry points in the Brillouin zone of a series of IV-IV, III–V, II–VI and I–VII semiconductors can be obtained accurately, to within 15%, from the Augmented Spherical Wave (ASW) method. The expression required for the evaluation of the matrix elements of the spin-orbit operator within the ASW basis set is derived and discussed. Our results imply that the earlier experimental assignment of Δ0′ for AlSb and InP should be reconsidered.

Ab inition determinations of oscillator strengths of metals and semiconductors from ASW

Abstract The evaluation of oscillator strengths from ab initio band structure calculations based upon the augmented spherical wave method (ASW) is outlined. From a detailed study for the metal Al, the direct semiconductor GaAs and the indirect semiconductor AlAs, we find excellent internal consistency between effective masses obtained from the band structure and the oscillator strengths, respectively. From a comparison with available experimental data for semiconductors we estimate the accuracy of our calculated oscillator strengths to be at the level of 20%. Across gap oscillator strengths for various semiconductors are given.

Oscillating Transverse Voltage in a Channel with Quantum Point Contact Voltage Probes

We have observed a transverse voltage on passing a current through a narrow channel, electrostatically defined in a two-dimensional electron gas, at zero magnetic field. The channel is fitted with two opposite quantum point contact voltage probes, and the voltage occurs when these probes are differently adjusted, so that the transmission probabilities through the probes have a different energy dependence. The transverse voltage occurs only in the nonlinear response regime, and is even in the applied current; the driving force of the effect is the current-heating of the electrons in the channel. We observe strong oscillations in the transverse voltage as the number of occupied subbands in one of the voltage probes is varied by means of electrostatic or magnetic depopulation. Model calculations show that this novel effect is a manifestation of the oscillatory thermopower of a quantum point contact predicted by Streda. The effect can thus be used to obtain information on electron heating.