T.G. van de Roer

Ionized impurity scattering in Monte Carlo calculations

A method to represent the effect of ionized impurity scattering in Monte Carlo calculations is presented. It is based on a model of B. K. Ridley [J. Phys. C 10, 1589 (1977)] and does not have the computational disadvantages of the Brooks–Herring and Conwell–Weisskopf models.

Polarization stabilization in vertical-cavity surface-emitting lasers through asymmetric current injection

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSELs.

Controlled polarization switching in VCSELs by means of asymmetric current injection

We have investigated the potential of asymmetric current injection for polarization switching in GaAs-based intracavity contacted vertical-cavity surface-emitting lasers using two sets of p- and n-type contacts per device. When using the contacts aligned along the [11~0] crystal direction, the observed laser polarization is parallel to [110], whereas, using the contacts along the [110] crystal direction, the polarization of the laser emission switches to a direction making an angle of 25/spl deg/-90/spl deg/ towards [110]. To overcome this peculiar result, a careful design of the contact layers in the intracavity structure is required.

Analysis of 6-nm AlGaAs SQW low-confinement laser structures for very high-power operation

This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-/spl mu/m-wide stripes was as high as 6.4 W before catastrophic optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 MW, which would mean a factor of 22.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm/sup -1/, in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm/sup 2/ for 5-mm-long devices in the symmetrical case and 2200 A/cm/sup 2/ in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed.

Self‐pulsating lasers with quantum well saturable absorber

Self‐pulsations are induced in broad area diode lasers by including an extra layer functioning as a saturable absorber. The absorption of this layer and its coupling to the photon field can be tuned via the layer thickness and its distance to the active layer. In the case of an Al0.13GaAs bulk active layer a GaAs absorber of 4 nm thickness at a distance of 0.2 μm induces stable oscillations with frequencies of 300–700 MHz in a current range just above the threshold.

Low-loss low-confinement GaAs-AlGaAs DQW laser diode with optical trap layer for high-power operation

A low-confinement asymmetric GaAs-AlGaAs double-quantum-well molecular-beam-epitaxy grown laser diode structure with optical trap layer is characterized, The value of the internal absorption coefficient is as low as 1.4 cm/sup -1/, while keeping the series resistance at values comparable cm with symmetrical quantum-well gradient index structures in the same material system. Uncoated devices show COD values of 35 mW//spl mu/m. If coated, this should scale to about 90 mW//spl mu/m. The threshold current density is about 1000 A/cm/sup 2/ for 2-mm-long devices and a considerable part of it is probably due to recombination in the optical trap layer. Fundamental mode operation is limited to 120-180 mW for 6.5-/spl mu/m-wide ridge waveguide uncoated devices and to 200-300 mW for 13.5-/spl mu/m-wide ones, because of thermal waveguiding effects. These values are measured under pulsed conditions, 10 /spl mu/s/l ms.

Influence of scattering on the I-V characteristics of double-barrier resonant-tunneling diodes

The influence of incoherent tunneling in double-barrier resonant-tunneling (DBRT) diodes, originating in carrier scattering, is investigated using a previously published model in which the device is divided into three regions (accumulation region, barrier region and depletion region), each of which is analyzed by a separate model. In the barrier region a self-consistent quantum mechanical model is used. Scattering is assumed to contribute a damped amplitude to the coherent wave function and the non-coherent carriers are assumed to tunnel out through one of the two barriers in proportion to the transmittivities of the latter. The damping factor can be related to the momentum relaxation time used in transport calculations. A good match of calculated to experimental I-V characteristics, measured on GaAs/AlGaAs DBRTs, can be obtained using a scattering time constant substantially shorter than that of bulk GaAs, indicating that there are extra scattering mechanisms to take account of.

Sealing method of dry etched AlAs/GaAs top mirrors in vertical cavity surface emitting lasers

A versatile sealing process for AlAs layers is presented. This sealing prevents the AlAs layers of AlAs/GaAs top distributed Bragg reflectors from further undesired oxidation during the wet oxidation of the AlAs current constriction layers in vertical cavity surface emitting lasers. This method has been successfully applied to protect the etched pillars in top mirrors although those pillars were plasma dry etched.

Controlled Anodic Oxidation for High Precision Etch Depth in AlGaAs III‐V Semiconductor Structures

Controlled anodic oxidation for achieving a better control of etch depth in AlGaAs semiconductor structures is studied. The rates of material consumption and oxide thickness growth for p ++ -GaAs and p-Al 0.38 Ga 0.89 As are given for the citric acid/glycol/water electrolyte. The etch profiles for GaAs/Al 0.45 Ga 0.55 As and GaAs/Al 0.50 Ga 0.40 As layer sequences in laser diode structures are presented. The underetch is rather high and depends on oxidation conditions (constant voltage or constant current). The profile obtained is very rough for constant voltage oxidation and much better when using constant current conditions. The latter also improves the uniformity of oxide growth. The etch rate of the anodic oxide in diluted HCl is much larger for GaAs than for AlGaAs.

Amplified spontaneous emission spectroscopy on semiconductor optical amplifiers subject to active light injection

It is shown that measurements of the effect of optical injection with an external laser on the spectral response of a semiconductor optical amplifier can probe intrinsic properties of a working device. The data demonstrate that under saturated gain conditions the carrier energy distribution within the active layer of a AlGaAs/GaAs amplifier neither shows spectral hole burning nor carrier heating, but only a decreased density.