M. Kubisa

Room temperature photoreflectance of MOCVD-grown InAs/GaAs quantum dots

Abstract Photoreflectance spectroscopy results are reported for InAs/GaAs self-organised quantum dots grown by low-pressure MOCVD. Quantum dot-related optical transitions have been observed for the first time at room temperature. Good agreement between experiment and theory based on a recent 8-band k·p theory has been obtained.

Impurity-related emission in the photoluminescence from p-type modulation doped Al1−xGaxAs/GaAs heterostructures

Abstract We investigated low-temperature photoluminescence from p-type Al1−xGaxAs/GaAs heterostructures. Our measurements show that at low laser power the H-band emission disappears and is replaced by a line resulting from the recombination of donor-bound electrons with two-dimensional holes. The properties of both lines are explained based on the results of detailed band structure calculations. Measurements in magnetic fields enabled us to examine the binding energy of donor in parallel electric and magnetic fields.

Photoreflectance spectroscopy of coupled InxGa1-xAs/GaAs quantum wells

Abstract The investigation of optical transitions in strained In 0.045 Ga 0.955 As/GaAs multiple quantum wells is presented. The structures were grown by molecular beam epitaxy for different GaAs barrier thickness (1, 3, 5 and 9 monolayers) and for different numbers of wells (3 and 4). The photoreflectance spectra of these samples have been measured at liquid nitrogen temperature. The origin of various spectral features have been assigned by using the results of the envelope function calculation and taking into account the effects of strain and exciton binding energy. The quantum wells are type I for the electron-heavy hole system and type II for the electron-light hole system, with the electrons and heavy holes confined in the In x Ga 1− x As layers and the light holes in the GaAs barrier regions. The influence of changes of barrier thickness on the confined transitions including parity-forbidden and indirect in the real space light hole ones has been studied. The splitting of the fundamental heavy hole state has been derived.

Optical Investigation of Coupled GaAs/Al0.3Ga0.7As Double Quantum Wells Separated by AIAs Barriers

Electronically symmetric coupled double quantum wells are structures where two quantum wells are separated by a thin barrier layer. Both experiment and theory show that when the barrier is so narrow that there is considerable overlap of wave functions in the two wells, the single quantum well electronic one-particle states split into symmetric and antisymmetric states with different energy levels. The splitting of energy levels is very sensitive to barrier width and barrier height and increases with decreasing barrier width and with decreasing barrier height.

Observation of excitons formed by the holes confined at the Al 0.5 Ga 0.5 As/GaAs interface

Abstract The radiative recombination in the Be-doped single heterojunction Al 0.5 Ga 0.5 As/GaAs, so-called H-band, has been studied by photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy. Magnetophotoluminescence measurements were also performed. The H-band was interpreted as the recombination of holes confined on the ground level in the quantum well at the interface and electrons from GaAs conduction band. The carriers involved in the recombination originate from 3D excitons excited in the flat band region of GaAs, which diffuse towards the interface. In the PLE spectra two new lines were observed. We interpret them in means of short life-time excitons composed of a confined 2D hole and a free electron, which are excited near the interface.

Photoreflectance study of coupling effects in double quantum wells

A double quantum well molecular beam epitaxy grown GaAs/AlxGa1-xAs structure was studied. To investigate the coupling effects in such a system 1 monolayer thick AlAs barrier was inserted at the center of the GaAs/AlxGa1-xAs single well. Due to the strong coupling between wells each confined state splits into two: symmetric and antisymmetric ones. In the room temperature photoreflectance spectrum features related to transitions between all these states were observed. Theoretical considerations based on the envelope function approximation were performed to obtain the energies of expected optical transitions. An excellent agreement between experiment and theory was obtained.

Investigations of interface excitons at p‐type GaAlAs/GaAs single heterojunctions in continues wave and time resolved magneto photoluminescence experiments

We report on investigations of polarisation resolved photoluminescence and photoluminescence excitiations from p‐type Ga1−xAlxAs/GaAs single heterojunctions in magnetic field up to 23 T. The observed excitonic type transitions are attributed to neutral excitons rather then to the charged ones.

Magneto-optical studies of 2D hole Landau levels and screening of donor states in p-type modulation doped Ga0.5Al0.5As/GaAs interfaces

We investigated low-temperature photoluminescence from p-type Al1−xGaxAs/GaAs heterostructures subjected to a magnetic field directed perpendicularly to the interface. Two observed type of structure related to interface transitions were interpreted as free (H-band) and donor-bound (D-line) electron recombinations with 2D holes. Properties of both type of structure were explained basing on the results of detailed band-structure calculations. Magnetic field measurements enabled us to examine the binding energy of donor screened by 2D holes in parallel electric and magnetic fields.

Excitons at the p-type modulation doped Al0.5Ga0.5As/GaAs interface

Two dimensional hole gas (2DHG) created at modulated doped Al1- xGaxAs/GaAs heterostructures was studied by optical methods. Samples of different 2DHG concentration p=9.8*1011 cm

Excited states of two-dimensional hole gas at the Al0.5Ga0.5As/GaAs interface

min2 were examined by means of photo luminescence (PL) and photo luminescence excitation (PLE) measurements under magnetic field up to 8T in Faraday configuration. In PL spectra two groups of lines are observed: a broad line at lower energy so called H-band and at higher energy exciton related lines. In magnetic field H-band splits and shifts linearly following Landau level quantization whereas higher energy lines exhibit diamagnetic shift. A strong absorption of H-band in PLE spectra is observed. We propose consistent theoretical model which explains both the nature of H-band and the formation of excitons on 2DHG states.