H.J.A. Bluyssen

Cyclotron resonance in an InAs-GaSb superlattice

Abstract Optical transmission in the far infrared region in an InAs-GaSb superlattice is studied as a function of magnetic field and frequency. Cyclotron resonance is observed for electrons confined in the InAs conduction band whose ground state is shifted to higher energy due to the periodic superlattice potential. These measurements confirm the calculated quantisation of the energy levels in a superlattice by ascertaining the effective mass directly.

Resonant polaron coupling of the n = 1 Landau level and the 2p+ donor state in GaAs

Abstract The n = 0 → > n = 1 Landau level and 1 s −2 p + impurity transitions in GaAs were investigated up to energies above the optical phonon energy ħΩ LO and d.c. magnetic fields up to 25 T. Pinning of both transitions to an energy slightly above and below ħΩ LO was observed. At an energy very close to ħΩ LO two additional impurity transitions are found. These features are attributed to the resonant polaron effect which leads to hybridization and dipole selection rule breakdown. Also the spin doublet splitting of both transitions were resolved showing a strong magnetic field dependence which can not be explained by nonparabolicity of the conduction band alone.

Mechanism of cyclotron-resonance induced conductivity in n-GaAs

Abstract A detailed mechanism is proposed and varified experimentally for Cyclotron Resonance Induced Conductivity (CRIC, cross modulation) at high magnetic inductions and low electric fields. The principal feature is thermal re-equilibration from donors to optically-depleted Landau levels, thus increasing carrier density. Cyclotron Resonance Induced Hall-effect (CRIH) measurements on n -type GaAs prove that CRIC originates from changes in carrier density and not in mobility as previously proposed. This mechanism also explains the observed temperature dependence of CRIC.

Effects of quantum confinement and compositional grading on the band structure of heterojunctions

Abstract The band structure of a heterojunction may have discrete electronic states arising from quantum confinement; in addition the band edge is perturbed by grading in the composition. A new method is introduced to analyse these effects by an effective field “Feff” in the transition region, including the position-dependence of space charge and of composition. The Feff is position-dependent and is zero-valued at the positions which correspond to extrema of the band edges. For most practical cases it is shown that Feff can be approximated as a linear function of position near the zero-valued positions, thus yielding harmonic oscillator states. The effective force constant can be expressed in terms of position-dependent material parameters. The effects of position-dependent effective masses are also considered. The analysis is applied to the p-n GaAsAl0.4Ga0.6As heterojunction; changes of the order of 1 10 eV in the effective band gap are predicted.

Ultrafast carrier dynamics at a metal-semiconductor interface studied by femtosecond luminescence spectroscopy

The ultrafast carrier dynamics in the high electric field at an Au-GaAs interface has been studied both experimentally, using a subpicosecond photoluminescence correlation technique, and theoretically by a Monte Carlo simulation. The photoluminescence decay time has been found to increase drastically with input power, ranging from a few picoseconds at low excitation to a considerably higher value (10-20 ps) at high excitation. From the Monte Carlo calculations it has been found that at high excitation the applied field collapses almost instantaneously. Even for a recharging time constant of 1 ps, which corresponds to the estimated device RC time, a drastic slowing down of the carrier sweep-out has been found, in almost quantitative agreement with the experimental findings.

Wavelength dependence of the emission of a double‐heterojunction GaAs‐AlGaAs injection laser in a strong magnetic field

The emission energy of continuously operated double‐heterostructure GaAs‐AlGaAs lasers has been measured in magnetic fields up to 15 T and temperatures of 4.2 and 50 K. For lasers with a p‐active region the observed shift in the emission energy can be described by a change in the position of the quasi‐Fermi level of the conduction band as a function of the magnetic field. The measurements provide a determination of the carrier density at threshold and verify the assumption that the matrix element for the optical transition is in first order independent of the applied magnetic field.

ULTRAFAST CARRIER DYNAMICS AT A METAL-SEMICONDUCTOR INTERFACE

The ultrafast carrier dynamics in the high electric field at an Au‐GaAs interface has been studied experimentally as well as theoretically. The photoluminescence decay time is related directly to the carrier sweepout from the GaAs depletion region, i.e., to the time needed for photoexcited electrons and holes to leave this region. This decay time has been found to increase drastically with laser input power, ranging from a few picoseconds at low excitation to values of 10–20 ps at high excitation. These results indicate a significant retardation of the sweepout, which cannot be explained by intervalley scattering and space‐charge effects. From our Monte Carlo calculations it has been found that the applied electric field collapses totally almost instantaneously after laser excitation due to the enormous excess of photoexcited charges. The sweepout only recovers after some time needed to recharge the device.

Determination of Landau-level lifetimes in n-GaAs

Abstract The lifetime of electrons in the first excited Landau level of n-GaAs is determined from a combination of measurements of far infrared cyclotron resonance induced absorption and conductivity change. Values of T1 of the order of 10−8s for densities of excited electrons of 1011 cm−3 and a temperature dependence of T−2.7 are found. An upper limit for the N = 0 Landau level to donor recombination time of the order of 10−9s was derived from pulsed conductivity measurements.

Radiative processes in the active layer of an injection laser studied in a strong magnetic field

Abstract The radiative processes and scattering mechanism of electrons in the very thin p-type active layer of a double heterojunction GaAs/AlGaAs injection laser have been studied. Measurements of the shift in the energy of the laser emission were made as a function of the magnetic field up to 25 T (DC) at low temperatures (T ≲ 40 K). The maximum of the gain curve has been calculated as a function of the magnetic field for radiative transitions in a p-type active layer, which occur between the occupied Landau levels in the conduction band and the unoccupied acceptors. The observed shift is in accordance with these calculations. From the measurements at very high magnetic fields, in which only the lowest Landau level contributes to the radiative emission, the carrier density at threshold and a temperature dependent scattering time for the electrons in the active layer is determined.

Hall‐effect determination of the N‐trap bound state in GaAs1−xPx

Hall‐effect measurements as a function of temperature on nitrogen‐containing GaAs1−xPx have shown that the nitrogen isoelectronic trap in these materials can be best described by a bound state in the band gap, occupied by electrons according to the equilibrium thermal distribution. It is shown that the presence of nitrogen can have a pronounced effect on the free‐carrier density. Our results are in excellent agreement with recent optical data.