Dependence of the Electroluminescence on the Spacer Layer Growth Temperature of Multilayer Quantum-Dot Laser Structures

Electroluminescence (EL) measurements have been performed on a set of In(Ga)As-GaAs quantum-dot (QD) structures with varying spacer layer growth temperature. At room temperature and low injection current, a superlinear dependence of the integrated EL intensity (IEL) on the injection current is observed. This superlinearity decreases as the spacer layer growth temperature increases and is attributed to a reduction in the amount of nonradiative recombination. Temperature-dependent IEL measurements show a reduction of the IEL with increasing temperature. Two thermally activated quenching processes, with activation energies of ˜ 157 meV and ˜ 320 meV, are deduced and these are attributed to the loss of electrons and holes from the QD ground state to the GaAs barriers. Our results demonstrate that growing the GaAs barriers at higher temperatures improves their quality, thereby increasing the radiative efficiency of the QD emission

High-performance three-layer 1.3-/spl mu/m InAs-GaAs quantum-dot lasers with very low continuous-wave room-temperature threshold currents

The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR)-coated facets has been utilized to obtain low threshold currents and threshold current densities for 1.3-/spl mu/m multilayer InAs-GaAs quantum-dot lasers. A very low continuous-wave (CW) room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm/sup 2/ are achieved for a three-layer device with a 1-mm HR/HR cavity. For a 2-mm cavity, the CW threshold current density is as low as 17 A/cm/sup 2/ for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets

1.3 µm InAs∕GaAs multilayer quantum-dot laser with extremely low room-temperature threshold current density

A high growth temperature step used for the GaAs spacer layer is shown to significantly improve the performance of 1.3 μm multilayer InAs/GaAs quantum-dot lasers. Extremely low room-temperature continuous-wave threshold current densities of 32.5 and 17 A/cm2 are achieved for a three-layer device with as-cleaved facets and high-reflectivity coated facets, respectively

Properties of non-polar a-plane GaN/AlGaN quantum wells

The structural and optical properties of a series of GaN/Al0.18Ga0.82N multiple quantum well (MQW) structures, in which the well thickness was varied between 2 and 8 nm, grown on a-plane (1 1 0) GaN on r-plane (1 0 2) sapphire substrates have been investigated. High-resolution X-ray diffraction and low-angle X-ray reflectivity measurements were used to determine the well and barrier thicknesses and the barrier composition after matrix transformation of the (binary) elastic constants for the appropriate coordinates, and assuming a pseudo-morphically strained system. The microstructure of the (1 1 0) samples is dominated by I1-type basal-plane stacking faults (BSF) terminated by partial dislocations or prismatic stacking faults, as determined by conventional and high-resolution transmission electron microscopy. The low temperature photoluminescence (PL) spectra of the QW structures show two emission bands which are assigned (partly based on photoluminescence excitation (PLE) spectroscopy) to excitons that are confined solely by the quantum wells and, at lower energy, those carriers that recombine in the region where the wells are intersected by BSFs. Both bands shift to higher energy with decreasing quantum well thickness. The optical data indicate that the non-polar (1 1 0) GaN/AlGaN system is free of polarization-induced electric fields, since the QW exciton emission energy is not below the band-edge emission energy of the GaN template

1-semiquasihomogeneous singularities of hypersurfaces in characteristic 2

In arbitrary characteristic different from 2, the singularities with semiquasihomogeneous equations characterized by the condition to have Saito-invariant 1 are the 'classical' quasihomogeneous ones, known over the field of complex numbers as simple elliptic singularities (Saito, [10]). Here we find them in characteristic 2 as well: In odd dimensions and for weights E_6 and E_8 non-quasihomogeneous equations appear. (orig.)Available from TIB Hannover: RR 6329(96-11) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman