M. Voos

Visible photoluminescence from porous silicon: A quantum confinement effect mainly due to holes?

We present results of photoluminescence experiments performed at 2 and 300 K on porous silicon layers with different porosities. The samples are obtained by electrochemical dissolution of (100) silicon wafers in hydrofluoric solution. The energy of the photoluminescence and its variation with porosity are found in good agreement with a theoretical model of quantum confinement in Si quantum wires. Electrons have to be taken into account, but it is shown that this quantum effect is mainly due (≊60%) to the large confinement of holes.

Growth of Ga0.47In0.53As-InP quantum wells by low pressure metalorganic chemical vapor deposition

We describe the growth of multiquantum well and single quantum well Ga0.47In0.53As‐InP structures by low pressure metalorganic chemical vapor deposition. The multiwell structure consists of 25‐, 50‐, 100‐, and 200‐A quantum wells (Ga0.47In0.53As layers) separated by 500‐A barriers (InP layers). Auger measurements indicate the presence of four distinct wells with abrupt boundaries. Photoluminescence measurements are consistent with the existence of four wells; however, deviations are noted between experimentally determined and theoretically predicted recombination energies. An analogous situation exists for the single (50 and 100 A) quantum well structures. Possible explanations, including variation of well composition, variation of well thickness, and participation of impurities in the recombination process are suggested.

Two‐dimensional electron gas in a In0.53Ga0.47As‐InP heterojunction grown by metalorganic chemical vapor deposition

We report, from Shubnikov‐de Haas and cyclotron resonance experiments, the first observation of a two‐dimensional, high‐mobility electron gas in a selectively doped In0.53Ga0.47 As‐InP heterojunction grown by metalorganic chemical vapor deposition. Several parameters of the electronic system under consideration are determined.

Raman scattering in GaSb‐AlSb strained layer superlattices

We observe that the energy of the GaSb longitudinal optical phonons in GaSb‐AlSb superlattices is about 2 cm−1 lower than in bulk GaSb. We show that this effect is fully explained by the consideration of the misfit strains which are known to exist in these superlattices. This shift of the Raman frequency allows a direct optical determination of the strains in heterostructures.

Optical studies of impurity trapping at the GaAlAs/GaAs interface in quantum well structures

We present low‐temperature photoluminescence studies of nominally undoped GaAs quantum wells in which weak acceptor‐related emissions can be observed. We investigate the influence of different sequences of prelayers, in which the number and the aluminum concentration of the layers are varied, on the impurity concentration in the quantum well, and show that thin layers of low aluminum percentage act as very efficient impurity trapping centers. We also present calculations of the electron to acceptor photoluminescence line shape, which show that the acceptor distribution has its maximum at the well interface, extending about 7 A in the barrier and 12 to 30 A in the well.

Bound and virtual bound states in semiconductor quantum wells

Abstract The bound and virtual bound (resonant) levels of GaAs-Ga(Al)As double quantum wells are calculated within the framework of the envelope function approach. The theoretical work, taken together with the results of excitation spectroscopy measurements, indicates the participation of a light hole virtual bound state in an optical transition.

Electron-hole drops in doped Ge

Abstract We investigate the radiative recombination of electron-hole drops in As and Sb doped Ge at about 2° K. Their luminescence spectrum exhibits a new zero phonon line whose study in As doped Ge suggests that this impurity gives rise to a virtual bound state in the electron Fermi sea.

Investigations of MOCVD-grown AlInAs-InP type II heterostructures

The authors report investigations of the low temperature optical properties of AlInAs-InP single heterojunctions and short period superlattices grown by atmospheric pressure MOCVD. Strong luminescence is observed and allows photoluminescence excitation measurements. Bandgaps are accurately determined from luminescence excitation and optical absorption spectra, and cross-checking optical data with structural properties yields a precise value (413 meV) of the conduction band offset in this system. This value deviates significantly from the prediction of the offset transitivity rule.

Observation of laser emission in an InP‐AlInAs type II superlattice

We report the observation of laser emission at low temperature from an optically pumped InP‐AlInAs superlattice grown by metalorganic chemical vapor deposition. Independent measurements of low level photoluminescence excitation and optical absorption show that laser emission occurs between spatially separated conduction and valence levels localized, respectively, in InP and AlInAs, with a calculated wave function overlap as low as 0.04. High radiative efficiency observed in this system is believed to be a genuine consequence of the type II band lineup.

Observation of double cyclotoron resonance and interband transitions in InAs-GaSb multi-heterojunctions

Abstract Magneto-absorption experiments are performed in an InAs-GaSb multiheterojunction where both electrons and holes are simultaneously confined at the interfaces. Oscillatory characteristics are observed and interpreted in terms of interband transitions from the single hole subband to the two lowest electron subbands, and of cyclotron resonances associated with these subbands. Two electron masses are obtained, arising directly as a consequence of the heterojunction potential.