A. Oster

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.

Diode lasers with Al-free quantum wells embedded in LOC AlGaAs waveguides between 715 nm and 840 nm

In this paper, we present results on diode lasers in the wavelength range between 715 nm and 840 nm with Al-free QWs which are embedded in a high-quality AlGaAs LOC broadened waveguide structure with low optical loss and a small vertical far field divergence. The laser structures were grown by LP- MOVPE. We studied tensile-strained GaAsP-QWs as well as compressively strained InGaAsP-QWs with strain compensating barriers. For lasers with GaAsP QWs, the lowest transparency current densities of about 130 A/cm2 were obtained in the wavelength range between 750 nm and 800 nm. Very low transparency current densities were achieved with InGaAsP-QWs at wavelengths above 800 nm. At 810 nm, high output powers (100 micrometer aperture) of about 7 W was achieved with both types of QWs from devices mounted epi up. However, with respect to high temperature operation and reliability tensile- strained GaAsP QWs seem to be the better choice, especially for the wavelength range below 760 nm.

Influence of current spreading on the transparency current density of quantum-well lasers

We investigate the dependence of the threshold current of broad-area lasers on the stripe width. A comparison of differently deep-etched devices fabricated from the same wafer reveals that the stripe width dependence of the threshold current is caused by the current spreading effect. We propose a simple method to obtain a transparency current density characterizing a particular epitaxial structure without being influenced by current spreading.

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.

Metalorganic vapor phase epitaxial growth of GaInAsP/GaAs

GaxAsyP1−y lattice matched to GaAs has been grown by low pressure metalorganic phase vapor epitaxy over the entire compositional range. At TG = 670°C broad peaks of low intensity are observed in the 10K photoluminescence for y = 0.2–0.4 due to the predicted miscibility gap in this compositional region. An increase in growth temperature leads to a smaller miscibility gap. The band gap as well as the morphology show a strong dependence on substrate misorientation. The smoothest GalnAsP surfaces are obtained on exact oriented substrates. For the ternary GalnP the surface roughness is correlated to the degree of ordering in the temperature range of 600 to 750°C. The smallest band gap together with the smoothest surface is obtained on (100) 2° off to (111)B. Ordering effects are also observed in the quaternary GalnAsP. Broad-area lasers processed from the grown layers show high slope efficiency (0.9 W/A) and low internal losses (<3 cm−1).

Photoluminescence on ordered GaxIn1−xAsyP1−y

Photoluminescence of Ga0.54In0.46As0.12P0.88 layers grown by metalorganic vapor phase epitaxy on differently oriented GaAs substrates has been investigated. Valence-band splitting due to symmetry breaking in ordered quaternary alloys was demonstrated by room temperature photoluminescence polarization spectroscopy. Single- and two-variant ordering was identified by high resolution x-ray diffraction on samples grown on (001) GaAs substrates misoriented 2° off to {111} B and on just oriented ones, respectively. The low temperature photoluminescence spectra consist of moving and nonmoving components, typical for ordered material. The blueshift of the moving component versus the pump level for the 0° samples is stronger than that for the 2°B samples. The full width at half maximum of the moving component increases with increasing injection level for the 0° samples, whereas it decreases for 2°B samples. We suppose that this different behavior of the low temperature photoluminescence observed on single- and two...

Interdiffusion in InGaAs/GaAs and InGaAs/GaAsP quantum wells

Abstract The shape of In0.22Ga0.78As single quantum wells (SQW) grown by metal-organic vapour phase epitaxy (MOVPE) is changed by rapid thermal annealing (RTA). Samples with GaAs barriers were compared with strain-compensated ones with GaAs0.82P0.18 barriers using high-resolution X-ray diffraction (HRXRD), Auger electron spectroscopy (AES) and photoluminescence spectroscopy (PL). After annealing, the PL wavelength is decreased and the luminescence intensity increased. In bare strain-compensated layers, In diffusion is slightly reduced at 850 °C annealing temperature. Encapsulation with SiO2 leads to an increase of the In diffusion up to a factor of 10. In this case, the diffusion process is dominated by vacancies and strain compensation is no longer effective.

Continuous-wave vertical-cavity surface-emitting lasers with emission wavelengths near 650 nm

Red VCSELs for emission wavelengths near 650nm find applications in emerging technologies such as plastic-fiber-based data communication. However, these devices are challenging due to low band offsets and high electrical and thermal resistivity of especially the p-DBR. The paper presents the optimization of p-DBR and QW design for the reduction of the series resistance and the threshold current density. VCSEL structures were grown using MOVPE and processed to air-post mesas. The resistance of the p:DBR mirrors was optimized using different dopants and interfaces. By changing from Zn doping and abrupt interfaces to the dopant C and introducing graded interfaces the differential resistance decreased. Due to a relative shift across the wafer between the DBR stop-band and gain peak wavelength defined by the MQW active region, devices are available with lasing wavelengths between 638nm and 662nm in pulsed-mode operation. Threshold current densities of 3.6kA/cm2 at 650nm are measured. For improving device parameters a current aperture was processed by selective wet oxidation of AlxGa1-xAs with varying x. Cw laser operation is achieved for wavelengths between 644nm and 657nm at 10°C ambient temperature. With threshold currents under 4mA maximum cw output powers of 160µW are obtained at wavelengths of 657nm and 650 nm.