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.

This paper reviews extensive Raman scattering, reflectance modulation and luminescence microprobe measurements made on GaInP/AlGaInP, GaAs/AlGaAs and InGaAs/AlGaAs ridge quantum well lasers to investigate (1) laser operating temperatures, (2) built-in mechanical stress, (3) atomic disorder in mirror facets, (4) Si recrystallization effects in mirror coatings, and (5) correlations of these parameters with laser performance and reliability data.

Summary form only given. This paper reports micro-Raman scattering investigations on GaInP/AlGaInP, GaAs/AlGaAs, and strained InGaAs/AlGaAs single quantum well (SQW) graded-index separate-confinement heterostructure ridge lasers. It demonstrates the potential and usefulness of Raman spectroscopy for optimizing the performance and reliability of laser diodes by measuring (i) local mirror temperatures, (ii) mechanical stress fields, (iii) mirror lattice disorder, and (iv) mirror coating stability under laser operation. Raman spectra have been measured in the backscattering geometry on the (110) facets of the 5-/spl mu/m-wide lasers by using the 457.9 nm Ar+ laser line with low powers of /spl sime/1 mW focused on a 1-/spl mu/m spot size. In this geometry only the transversal-optical (TO) phonon modes are allowed.

We report stress measurements on Al0.04Ga0.96As/Al0.44Ga0.56As single quantum well laser diodes with 5-mu m-wide ridge waveguides. Raman scattering and photoluminescence microprobe spectroscopy have been employed to measure the stress distribution in the ridge region on the cleaved, uncoated (110) mirror facets and to identify the stress sources. The camel hump-like stress profiles along the active layer show compressive stress with maximum amplitudes of 4 kbar near the ridge slopes and with reduced amplitudes close to. the ridge center. Both the ridge-embedding Si3N4 layer and the top p-metallization introduce strain. Model experiments with externally applied stress of up to approximate to 1 kbar demonstrated the high sensitivity of the laser near field and threshold current to stress fields. They also allowed the measurement of:low built-in stress amplitudes as small as 50 bar.

High-reflective PECVD Si/Si3N4 and IB Si/Al2O3 back facet coating stacks of MBE-grown, strained InGaAs/AlGaAs GRINSCH-SQW, 4-mu m-wide ridge-waveguide lasers exhibit distinctive properties under laser output power. Raman microprobe spectra show that PECVD Si layers remain amorphous independent of exposure time and power applied, whereas IB Si layers rapidly recrystallize within hours and at lower power levels. Local mirror temperatures are approximate to 2x higher in the IB stacks than in the PECVD stacks. The refractive index of IB Si changes from 3.85 to 3.45 at 980 nm according to a transition from amorphous to crystalline Si. This reduces the reflectivity of the stack from 95 to 91%, and increases the power transmitted by the back facet by a factor of 1.7. Model experiments employing a controlled local recrystallization by external Ar+ laser irradiation showed that recrystallization has an impact on near-field patterns and on nonlinearities in the light-current characteristics.

Reflectance modulation measurements on red-emitting GaInP quantum well ridge lasers show a sensitive dependence of the laser mirror temperatures on the number of quantum wells, the type of cladding layers, the configuration of a heat spreader layer covering the ridge waveguide, and on how the laser is mounted on a heat sink. The temperature versus injection current curves also demonstrate the contribution of laser radiation heating even in single quantum well lasers. The temperatures decay rapidly from the mirror into the cavity within about 6 μm (1/e-point) as found from spatially resolved electroluminescence spectra detected along the laser cavity.

Thermoreflectance measurements performed for the first time on laser diode mirrors have supplied a vast amount of novel information. Heating efficiency has been found to depend sensitively on the mirror treatment, the mirror structure design, the geometry of a deposited heat spreader, the type of coupling of the laser to a heat sink, the number of active quantum wells, the type of cladding layer and the strength of lattice disorder at the mirror surfaces. Degradation processes have been observed in real time by continuously monitoring the mirror temperature. Dark line defects formed during laser operation exhibit a temperature gradually increasing with time. The mirrors suffer catastrophic optical damage within seconds after having reached a critical temperature. Temperature maps show a striking localized hot spot within the optical near-field pattern.

We report on growth investigations and results of low threshold current density GaInAsP/InP multiple quantum well (MQW) lasers emitting at a wavelength of 1.3 μm. Bulk layers and separate confinement heterostructure MQW laser diodes were grown by chemical beam epitaxy. At optimized growth conditions, broad-area lasers with as low a threshold current density Jth as 160 A/cm2 and an internal loss of 5 cm-1 were obtained.

Raman microprobe spectra from dry-etched, coated (110) AlGaAs single quantum well laser mirrors show, apart from the allowed phonon modes, a series of symmetry forbidden modes whose strength is dependent on the mirror treatment prior to coating. A particularly strong mode at 193 cm−1 can be attributed to disorder activated longitudinal acoustic phonon scattering in addition to—and this is new—the Eg-mode of elemental arsenic. The existence of lattice disorder and arsenic clusters is confirmed by Rayleigh scattering and energy dispersive x-ray spectroscopy. The optical power level at catastrophic optical mirror damage and the local mirror temperatures of the biased laser are found to have a strong dependence on mirror disorder.

A nonabsorbing etched mirror structure for AlGaAs SQW-GRINSCH ridge lasers is discussed with respect to mirror coupling coefficient, threshold current penalty, farfield pattern, fourfold catastrophic optical power level improvement, and mirror temperature.

Temperature rises were measured on cleaved, uncoated mirror facets of junction-side-up mounted (Al)GaInP laser diodes as a function of the injection current by Raman spectroscopy via the Stokes/anti-Stokes phonon line intensity ratio and the phonon line shift as well as by reflectance modulation as a novel application for laser mirror characterization. Below the threshold current the temperature rise is due to Joule heating of the drive current across the ohmic resistor and is ΔT≂35 K at threshold. Above threshold a significant power-dependent heating caused by absorption of laser radiation is superimposed. In this regime the temperature increase is considerably high, i.e., ΔT≥100 K at 4 mW for 5-μm-wide ridge lasers. The different measurement techniques have produced consistent data.

Keywords: Alxga1-Xas Reference EPFL-CONF-164911View record in Web of Science Record created on 2011-04-11, modified on 2017-05-10

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 have investigated the susceptibility of laser structures to the formation of electrically active defects. In particular, we have searched for "weak spots" on the mirrors of ridge-waveguide GaAs/AlGaAs quantum well lasers; firstly, by measuring mechanical strain distributions by micro-Raman spectroscopy and, secondly, by exposing the mirrors to electron irradiation in a scanning electron microscope (SEM) to activate the formation of defects monitored by electron beam-induced current (EBIC). Raman line scans reveal a strain of about 2 kbar close to the ridge edges. This location coincides with regions where the EBIC signal strongly changes in space. Migration and spatial separation of native defects in a strain field may account for the latter effect.

Spatially-resolved light reflectance modulation (RM) measurements on mirrors of GaAs/AlGaAs lasers show that the change of normal-incidence reflectance DELTA-R/R increases with optical output power. Below the lasing threshold, DELTA-R/R is due to electroreflectance caused by a reduction of the surface potential by carrier injection, whereas above threshold, it increases with a strength strongly dependent on the mirror technology used. Temperature maps exhibit a very localized hot spot around the active layer, with the temperature dropping sharply outside within a few microns. Compared to Raman spectroscopy, RM offers numerous advantages.

The diffusion and desorption of Ga atoms in MBE-grown AlGaAs layers and GaAs QWs on channeled substrate planar structures have been studied by scanning electron microscopy, photoluminescence and cathodoluminescence. The (m11)A side facets of ridges and grooves act as sources for additional Ga which increases the growth rate on the (100) sections of ridges and grooves, leading to lower Al compositions and thicker quantum wells on narrow stripes. The adatom flux is increased for growth temperatures above 700°C and an As4:(Ga,Al) flux ratio below 1. Growth interruption after the QW leads to a complete desorption of Ga at the (311)A facets, leaving an embedded (100) QW.

Deep-level-transient spectroscopy on molecular-beam epitaxially grown square GaAs/ n-AlxGa1−x As (x=0.24–0.39) single-quantum wells shows a series of electron traps in the AlGaAs with energies EC−ET at 0.12, 0.22, 0.29, 0.52, and 0.63 eV and with concentrations of about 5×1015 cm−3. The defects are located in the upper AlGaAs layer near the GaAs well layer. The trap concentrations and the widths of the spatial trap distributions (typically 15 nm) are independent of the well width. For all traps, a nonexponential capture process which is logarithmic in time is observed. Time-dependent depth profiling shows a virtual shift of the trap distribution to the surface for shorter filling pulses. Both effects are due to the nonabrupt depletion edge (Debye tail). No direct emission from the quantum wells is observed.