S. Gramlich

12 W continuous-wave diode lasers at 1120 nm with InGaAs quantum wells

Highly strained InGaAs quantum wells were grown by metalorganic vapor-phase epitaxy. By lowering the growth temperature to 530 °C, a maximum photoluminescence wavelength of 1192 nm was achieved. High-power diode lasers with a maximum lasing wavelength of 1175 nm were fabricated. A continuous-wave output power of 12 W at a heat-sink temperature of 25 °C was obtained at a lasing wavelength of 1120 nm.

Influence of the growth temperature and substrate orientation on the layer properties of MOVPE-growth (Ga,In)(As,P)GaAs

Abstract The luminescence properties of In 1− x Ga x As y P 1− y layers and heterostructures grown lattice matched to GaAs by metalorganic vapour-phase epitaxy (MOVPE) were studied and correlated to the crystalline properties. For laser structures emitting around 800 nm a red-shift of the emission from the active layer ( y = 0.72) grown at 680°C together with an anomalous temperature behaviour and excitation dependence of the bandgap is observed. Although some degree of ordering is observed for thick layers of this composition, polarization dependent photoluminescence does not indicate ordering of the quantum well to be the main reason for this excitation dependence. Instead, interfacial In-rich layers are found to be responsible. The thickness of these interfacial layers strongly depends on substrate misorientation and growth conditions.

Effect of growth interruption on performance of AlGaAs/InGaAs/GaAs quantum well lasers

Abstract The effect of a growth interruption at the interfaces of the AlGaAs/InGaAs/GaAs quantum well (QW) in the active region of metalorganic vapour phase epitaxy (MOVPE) grown 980 nm laser diodes has been studied. Characterization of the layer structures by photoluminescence, photoluminescence decay and cathodoluminescence shows the necessity for a growth interruption of 10–20 s. This is consistent with the results obtained on broad area lasers that show very low threshold current densities and internal losses for such interruption times.

Direct Growth of GaN on (0001) Sapphire by Low Pressure Hydride Vapour Phase Epitaxy

A two-step process for GaN on (0001) sapphire based on low-temperature GaN nucleation in low pressure hydride vapour phase epitaxy using a conventional reactor is described. The process allows reproducibly for subsequent growth of high-quality GaN layers eliminating the need for ex-situ pregrowth processes like sputtering of ZnO or use of MOVPE-grown templates. By means of electron microscopy and thin film X-ray diffraction it is shown that the nucleation procedure yields high-density nucleation centers of the same orientation as the substrate and promotes the lateral growth of epitaxial GaN films.

Electric field-induced redistribution of free carriers at isotype (In,Ga)P/GaAs interfaces

Metal–semiconductor contacts are applied to study depth-resolved electrical characteristics of Si- and Zn-doped GaAs/ (In,Ga)P/GaAs heterojunctions by capacitance–voltage measurements. The measured depth profiles of the carrier concentration are compared with calculations based on solutions of the Poisson equation. Different growth conditions are chosen in order to produce heterointerfaces with (In,Ga)P layers of various degrees of order. It is shown that (In,Ga)P ordering induces piezoelectric polarization charges at interfaces with GaAs, the density of which increases with higher degree of order. The related electric field results in a redistribution of free carriers. For weakly ordered (In,Ga)P, the interfaces are found to be of type I.

Minority-carrier kinetics in heavily doped GaAs:C studied by transient photoluminescence

Room-temperature photoluminescence decay time measurements in heavily doped GaAs:C-layers designed as base layers for heterojunction bipolar transistors are reported. These measurements provide access to nonequilibrium minority carrier lifetimes that determine the current gains of those devices. By systematically studying transient luminescence spectra over a wide range of excitation densities between 1013 and 1018 cm−3, we demonstrate the importance of carrier trapping processes at low excitation densities. Optimized excitation conditions that achieve trap saturation but also avoid stimulated emission are found for densities of (1–3)×1017 cm−3/pulse. Detection is limited to a spectral window well above the energy gap (beyond 1.5 eV). Values for both Auger and radiative recombination coefficients are given.

Evidence for strain-induced lateral carrier confinement in InGaAs quantum wells by low-temperature near-field spectroscopy

A strain-induced lateral variation of the band edges of a 10-nm-thick In0.16Ga0.84As quantum well embedded in GaAs is achieved by patterning of a 100-nm-thick compressively strained In0.52Ga0.48P stressor layer. The strain modulation results in a splitting of the 10 K far-field photoluminescence (PL) spectra into two emission peaks. Spectrally resolved two-dimensional near-field PL images establish a clear spatial and spectral separation of the two far-field PL peaks, indicating a lateral carrier confinement with a confinement energy of about 10 meV. Finite-element calculations of the strain distribution are used to determine the lateral band-edge shifts and are well in agreement with the experimental findings.

Evaluation of strained InGaAs/GaAs quantum wells by atomic force microscopy

Atomic force microscopy (AFM) is adopted for evaluation of strained InGaAs/GaAs quantum well structures grown by metalorganic vapor phase epitaxy. InAs-rich clusters are formed at the upper interface when the structure is grown with excessive supply of the In precursor. The defects arising from the clusters are clearly observed as convex domains from the irregularity of monolayer steps. The density of the convex domains coincides with the dark spot density measured by cathodoluminescence. Photoluminescence intensity is drastically reduced at high density of this type of defects. Thus, AFM measurements are able not only to give information on the structural quality but also to provide an estimation of the optical quality of such InGaAs/GaAs structures.

High-resolution X-ray diffraction investigation of crystal perfection and relaxation of GaAs/InGaAs/GaAs quantum wells depending on MOVPE growth conditions

SummaryThe influence of growth conditions and the concentration of indium in the vapour phase on the crystal perfection of strained InGaAs/GaAs quantum wells grown by metalorganic vapour phase epitaxy is studied by high-resolution X-ray diffraction, cathodoluminescence, photoluminescence and transmission electron microscopy. A strong dependence of the misfit dislocation density on the growth temperature is found. With increasing In concentration in the vapour phase a transition to the 3-dimensional growth mode leading to a different type of defect formation is observed.

Assessment of compensation ratio in high-purity GaAs using photoluminescence

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. The compensation ratio in high-purity n-type GaAs layers grown by metal−organic vapour phase epitaxy was determined from low-temperature photoluminescence measurements using the intensity ratio of the acceptor- and donor-bound excitonic transitions. The compensation ratio decreases with increasing V−III ratio. At high V−III ratio, a total acceptor content of below 1×10 13 cm −3 is found.