Spatially resolved Raman scattering measurements (<1 μm) have been performed to determine the surface temperature distribution on coated and uncoated facets of ridge-waveguided GaAs/AlGaAs single quantum well graded-index separate-confinement heterostructure lasers. A strong nonlinear temperature versus output-power dependence is observed for cleaved, uncoated mirrors (ΔT>100 K for P>1 MW/cm2). Raman line scans show hot spot regions at the facets. Degradation strength correlates with facet heating. Disorder-activated Raman phonon modes indicate strong crystal damage. Laser mirrors with λ/2-Al2O3 coatings withstand up to 4–5 times the power density without significant heating and degradation. Local electroluminescence measurements along the cavity confirm increasing temperatures when approaching the facets and show that the resonator bulk material remains cold (ΔT<5 K).

We report the optical and structural properties of ion implanted GaN:Zn. Post-implant annealing up to 1100 °C was performed under flowing N2 in both a tube furnace and a rapid thermal annealing (RTA) system, with and without SiNx encapsulation layers. The implantation damage is quantified by transmission electron microscopy (TEM). Secondary ion mass spectroscopy (SIMS) detects significant rearrangement of implanted Zn only at the highest temperatures and doses investigated. Strain reduction, observed in GaN:Zn annealed at or above 975 °C by high-resolution x-ray diffractometry (HRXRD), indicates successful damage removal. The optical activation of annealed GaN:Zn is measured by photoluminescence (PL). The room temperature (RT) Zn acceptor transition at ∼430 nm is consistently observed in annealed GaN:Zn, but at low efficiency. We conclude that residual implantation damage and/or N loss during annealing limits the optical quality of implanted GaN:Zn.

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In Sn-I-Sn-I-Pb tunneling structures the energy gap ~Sn of Sn is reduced by quasiparticle injection via single-particle tunneling between the Sn films. ~Sn as function of the quasiparticle density is probed by the Pb contact and found in agreement with the theory of OWen and Scalapino. An instability of the energy gap of Sn is observed at the critical gap reduction ratio predicted by this theory for a first-ortler phase transition.Nonequilibrium quasiparticle distributions in superconductors can be produced by photon l -3 and phonon 4 irradiation or by quasiparticle 5 injection via tunneling. Under constant injection conditions the stationary quasiparticle energy distribution is determined by the energy distribution of the primary quasiparticle injection or excitation rates, by the energy dependence of relaxation and recombination probabilities, and by secondary quasiparticle excitation and pair-breaking rates via phonon absorption. Since phonons are emitted in quasiparticle decay, the phonon escape probability from the superconducting film into the substrate and the intrinsic phonon decay also have a strong influence on the stationary quasiparticle energy distribution. Whereas the general problem of the quasiparticle distribution can be solved numerically,6 two important simple models have been discussed in the past: For the limit of recombination lifetimes long compared to relaxation times, Owen and Scalapino 7 proposed a nonequilibrium quasiparticle distribution in which the excess number of quasiparticles is characterized by a chemical potential p* > 0 and their energy distribution by the unperturbed lattice temperature T. Since most superconducting films show high phonon trappingS by pairbreaking, Parker 9 proposed a model in which an elevated temperature T* > T describes the number of quasiparticles and their energy distribution. A significant difference between the two models is that the "/1* model" predicts a first-order phase transition as the number of excess quasiparticles is increased, whereas the "T* model" does not. Different experiments with optical excitation of quasiparticles 2 ,3.1o did not give clear evidence in favor of one of the two models.In this communication we report on experiments with quasiparticle injection via tunneling between two Sn films and probing the energy gap and the quasiparticle population with a Pb contact. In accord with the 11-* model we find that the gap reduction as function of the quasiparticle density is stronger than in the thermal case and we observe an instability of the energy gap at the predicted critical gap reduction.The sample consists of two overlapping Sn films and one Pb film, width and thickness of each film being 1.4 mm and 1000 A, respectively (Fig. 1).Silicon single crystals are used as substrates which are cooled by direct contact to the liquidHe bath on the backside. The front surface with the Sn-J-Sn-J-Pb structure can be kept under vacuum or also exposed to liquid He. By 15-min glow-discharge oxidation in O 2 at 100 mTorr the tunneling resistance ...

We have measured the temperature dependence of the effective quasiparticle recombination time in superconducting tin tunnel junctions by current and laser pulse excitation. The experimental times show satisfactory agreement with calculations based on the ray acoustic lifetime model of Eisenmenger et al. taking into account the film thickness dependence of the phonon reabsorption, 2A-phonon volume loss processes and phonon transmission from the junction into the substrate and liquid helium. On the basis of the BCS density of thermally excited quasiparticles and simplified rate equations for quasiparticle recombination, and from the analysis of measurements of decaying excess quasiparticle concentrations we obtain a mean value N o =(2.73_+0.03) 1022 eV-1 cm-3 for the electronic density of states at the Fermi Surface in thin, evaporated tin films. This value differs less than 5 % from that obtained from the experimental electronic heatcapacity coefficient of the bulk material.