Sebastian Mogg

Temperature sensitivity of the threshold current of long-wavelength InGaAs-GaAs VCSELs with large gain-cavity detuning

Record-long emission wavelengths up to 1.3 /spl mu/m have recently been demonstrated from highly strained InGaAs-GaAs double-quantum-well (DQW) vertical-cavity surface-emitting lasers (VCSELs). The operation of InGaAs VCSELs at such long wavelengths has relied on a large detuning between the spectral positions of QW gain maximum and cavity resonance. This detuning also affects the high-temperature performance and temperature sensitivity of such devices. In this paper, we present and evaluate the threshold current-temperature characteristic of such lasers in relation to the gain-cavity detuning at room temperature (RT). For a near-zero gain peak offset from the emission wavelength at RT, the minimum threshold current is found at the temperature where the gain peak wavelength and the cavity resonance are approximately aligned. This is well in line with a common design rule for GaAs-based VCSELs. However, we show that this design rule fails in the case of larger gain-cavity misalignment at RT. Instead, a minimum threshold current is obtained considerably below the temperature of zero gain offset. We propose a conceptual model that relates the gain-cavity detuning at RT to the temperature sensitivity of the active region performance, which qualitatively describes the threshold current-temperature characteristic typical of VCSELs. The results demonstrate the importance of improving the temperature characteristic of the active region in order to reduce the high temperature sensitivity of devices with large detuning.

Properties of highly strained InGaAs/GaAs quantum wells for 1.2-μm laser diodes

The properties of 1.2-μm highly strained InGaAs quantum wells (QWs) grown on GaAs substrates have been analyzed. Optical gain spectra versus injection current and temperature, transparency current density, as well as other figures of merit were assessed from measurements on broad-area and ridge-waveguide lasers based on these QWs. Such active regions are of interest for a range of applications, including GaAs-based high-power lasers and vertical-cavity lasers for wavelengths beyond 1.2 μm.

Doping-induced losses in AlAs/GaAs distributed Bragg reflectors

We have studied n- and p-type doping-induced performance degradation of AlAs/GaAs distributed Bragg reflectors (DBRs) for applications in vertical cavity lasers (VCLs). Based on high-accuracy optical reflectance and triple-axis x-ray diffraction measurements on a variety of differently doped DBR structures grown by metalorganic vapor-phase epitaxy, a fitting procedure was employed to extract the doping-dependent optical loss. A striking observation is that the reflectance of these DBRs is much more sensitive to n- than p-type doping incorporation. While in the latter case the loss can be well accounted for by intervalence-band and free-carrier absorption, additional loss mechanisms must be considered for n-type DBRs. We relate the losses to doping-enhanced interdiffusion effects resulting in increased interface scattering. These findings should have important consequences for the design of VCLs, demonstrating the importance of reduced n-type doping concentrations and/or growth temperatures, or the applica...

Low-Temperature Metal-Organic Vapor-Phase Epitaxy Growth and Performance of 1.3-µm GaInNAs/GaAs Single Quantum Well Lasers

GaInNAs/GaAs quantum-well (QW) lasers emitting at 1.3 µm were grown using metal-organic vapor-phase epitaxy (MOVPE) in the limit of very low growth rate and temperature. The material was characterized by photoluminescence (PL) Spectroscopy as well as by implementation in broad-area (BA) edge-emitting lasers. While the PL intensity was found to decrease by more than two orders of magnitude between 1175 and 1350 mn, the corresponding BA laser threshold current showed a much more modest increase. For a 1.28-µm laser the threshold current was 1.2 kA/cm2 (1200 µm long devices), with a slope efficiency 0.24 W/A per facet and T0=100 K. Comparison between PL emission properties and BA laser performance revealed a complex relationship. A high PL intensity does not necessarily lead to low threshold-current lasers. In these cases, the FWHM seems to be the more relevant parameter for QW optimization.

All-Epitaxial Single-Fused 1.55 µm Vertical Cavity Laser Based on an InP Bragg Reflector

We have realised an all-epitaxial 1.55 µm vertical cavity laser by employing a single wafer-fusion step. The laser structure is fabricated by fusing a 32-period p-doped (C) AlGaAs/GaAs top mirror onto a half-cavity structure consisting of a 50-period n-doped (Si) GaInAsP/InP bottom mirror and a 9 quantum well GaInAsP-active material. Laser mesas are fabricated using a wet etching procedure for the top mirror. The top mirror also contains an AlAs layer for oxidation for current confinement. The lasers operate pulsed at temperatures up to 40°C and at pulse lengths of 10 µs up to 5°C. The minimum threshold current density at room temperature is 1.8 kA/cm2 for a device diameter of 55 µm. Compared to nonoxidised laser diodes, the threshold current is markedly decreased in oxidised laser diodes.

Optimization of the barrier height in 1.3-μm InGaAsP multiple-quantum-well active regions for high-temperature operation

We present a study of barrier height effects on the high-temperature performance of 1.3 micron strained layer InGaAsP/InP quantum well lasers. Broad-area Fabry-Perot lasers were fabricated and their light-current characteristics were measured at temperatures between 20 degrees C and 80 degrees C. Based on our experimental results we analyze the effect of the barrier bandgap using the commercial laser simulation software LASTIP. The simulator calculates all relevant physical mechanisms, including their dependence on temperature and local carrier density, self-consistently. The strained quantum-well optical gain computation is based on the 4 x 4 kp method considering valence-band mixing effects. A drift-diffusion model including thermionic emission at hetero-interfaces is used for the calculation of the carrier transport. Careful adjustments of material parameters, in agreement with data reported in the literature, are performed in order to reproduce the measurements. Lowering the barrier height in the active region leads to an improved performance of our laser with respect to threshold current and slope efficiency. An optimum barrier bandgap range of 1.21 - 1.24 eV is identified for our laser. This is partially attributed to the non-uniform carrier-distribution across the quantum-wells.

Single-mode 1.27 μm InGaAs vertical cavity surface-emitting lasers with temperature-tolerant modulation characteristics

The dynamic performance of InGaAs/GaAs 1.27 m m single-mode vertical cavity surface emitting lasers (VCSELs) is presented. In order to reach such a long wavelength, the devices utilize highl ...

1300-nm GaAs-based vertical-cavity lasers

We compare GaInNAs and highly strained InGaAs quantum-wells (QWs) for applications in metal-organic vapor-phase epitaxy (MOVPE)-grown GaAs-based 1300-nm vertical-cavity lasers (VCLs). While the peak wavelength of InGaAs QWs can be extended by a small fraction of N, the luminescence efficiency degrades strongly with wavelength. On the other hand, using highly strained InGaAs QWs in combination with a large VCL detuning it is also possible to push the emission wavelength towards 1.3 μm. The optimized MOVPE growth conditions for such QW and VCL structures are discussed in some detail. It is noted that GaInNAs and InGaAs QWs preferably are grown at low temperature, but with quite different V/III ratios and growth rates. We also point out the importance of reduced doping concentration and growth temperature of the n-doped bottom DBR to minimize optical loss and for compatibility with GaInNAs QWs. InGaAs VCLs with emission wavelength beyond 1260 nm is demonstrated. This includes mW-range output power, mA-range threshold current and 10 Gb/s data transmission.

1.3-ÎŒm InGaAs(N)/GaAs vertical-cavity lasers

In this work we present performance characteristics of metalorganic vapor-plase epitaxy grown GaInNAs and InGaAs quantum-well (QW) vertical-cavity lasers (VCLs) for 1.3-μm applications. The InGaAs VCLs emit in a wavelength range from 1200 to somewhat above 1260 nm, while the GaInNAs VCLs operate from 1264 to 1303 nm. The InGaAs VCLs are based on highly strained InGaAs double QWs, with photoluminescence (PL) maximum around 1190 nm, and extensive negative gain-cavity detuning. As a consequence, these devices are strongly temperature sensitive and the minimum threshold current is found at very high temperature (~90-100°C). Both kind of VCLs work continuous-wave well above 100°C, and while the InGaAs VCLs reach slightly higher light output power, they show significantly larger threshold currents. In addition, the large device detuning also has profound effects on the high-frequency response. Nevertheless, for a 1260-nm device, 10 Gb/s transmission is demonstrated in a back-to-back configuration. We also show that by further optimization of the InGaAs QWs the PL peak wavelength can be extended to at least 1240 nm. The incorporation of such QWs in the present VCL structure should considerably improve the device performance, resulting in higher light output power, lower threshold current, and reduced temperature sensitivity with a shift of the minimum threshold current towards room temperature, thus approaching standard VCL tuning.

High-performance 1.2-/spl mu/m highly strained InGaAs/GaAs quantum well lasers

The growth and characterisation of high-performance 1.2-/spl mu/m highly strained InGaAs/GaAs single quantum well (SQW) laser diodes is reported. High output power in excess of 200 mW per facet was obtained from ridge-waveguide (RWG) lasers at an emission wavelength of 1230 nm. These lasers operate CW to at least 145/spl deg/C and show a high characteristic temperature of 150 K. The net modal gain was measured using the method described by Hakki and Paoli (1975).