Eberhard Veuhoff

Fabrication of AlGaInAs and GaInAsP buried heterostructure lasers by in situ etching

Abstract We present a novel modified technique of in situ etching with tertiarybutyl chloride (TBCl) which allows etching of both, GaInAsP/InP and AlGaInAs/InP structures for the fabrication of buried heterostructure (BH) lasers in an MOVPE system. It is shown that the surface morphology is improved, when small amounts of trimethyl gallium are injected during TBCl etching at reduced reactor pressure. The etching process is performed in a PH 3 -free atmosphere under hydrogen. Therefore, the etching temperature has to be kept at the relatively low value of 580°C. GaInAsP and AlGaInAs MQW laser ridges can be formed by in situ etching under identical reactor conditions (pressure, temperature, precursor flow). For Al containing layers, however, an ex situ wet chemical etch dip is additionally required in order to avoid residue deposition which results in deteriorated surface morphology. High-quality GaInAsP and AlGaInAs ridges for BH laser applications are obtained. GaInAsP/InP BH lasers fabricated by this technique exhibit excellent high-temperature characteristics.

High Performance 1.55 µm Quantum-Well Metal-Clad Ridge-Waveguide Distributed Feedback Lasers

We present results on high performance 1.55 µm InGaAs/InGaAsP multiple quantum well metal-clad ridge-waveguide distributed feedback lasers. The multilayer structure was grown entirely by low pressure metal-organic vapor phase epitaxy. For improved high speed modulation a small-area contact mask was used. As a result the following characteristics were obtained on the same device: 38 mW single-mode output power with a 3dB-bandwidth of 11 GHz and a linewidth of 3.5 MHz. Best values for the individual parameters are 71 mW, 11 GHz and 880 kHz.

Comparison of structural and optical properties in strained GaInAsP MQW structures grown by MOVPE and MOMBE

Abstract The growth parameter dependence of the transition from 2D to 3D growth of GaInAsP multiple quantum well (MQW) structures up to e B =0.5% tensile-strained barriers was examined. Identical MQW structures with e W =1% compressively strained wells were grown by metal organic vapor-phase epitaxy (MOVPE) and metal organic molecular beam epitaxy (MOMBE) and characterized by photoluminescence (PL), X-ray diffraction and transmission electron microscopy. Increasing the tensile barrier strain resulted in deteriorated optical and crystalline properties beyond a critical strain limit, which depends on growth temperature. The deterioration originates from lateral layer thickness and strain modulations. Their density, amplitude and thus their effect on the optical MQW properties are different for both growth methods. High-quality MOMBE-grown MQW structures up to e W =2% compressive well strain and e B =0.5–1% tensile barrier strain could be achieved by inserting thin intermediate layers at each internal interface. The composition of these intermediate layers has a significant effect on MQW material properties.

Leakage Current Reduction in Buried Heterostructure Tunable Twin-Guide Laser Diodes

An effective concept for leakage current reduction in tunable twin-guide (TTG) lasers is proposed. TTG lasers fabricated according to this modified design using a hybrid metalorganic vapour phase and liquid phase process achieve CW output power exceeding 25 mW and linewidth below 10 MHz within the tuning range of 2 nm.

In-situ etching of InP based BH laser structures in MOVPE

Tertiarybutylchloride (TBCl) was used for etching of InP based buried heterostructure (BH) laser ridges in an MOVPE system. Applying this in-situ technique with subsequent regrowth will increase process yield and reliability. Etch rates are directly proportional to the TBCl flow. Increasing the hydrogen carrier gas flow yields decreased etch rates, these can be increased at higher temperatures. An excellent surface morphology is essential. This can be obtained under conditions favoring a high surface diffusion. It was found that a PH/sub 3/-free etching process at 580 /spl deg/C leads to best results both, for InP and GaInAsP layers. An increasing Ga content decreases the etch rate, especially in a PH/sub 3/-free process. Smooth {111} planes are formed during TBCl etching under optimized conditions. For the first time this process was successfully utilized to produce BH lasers. Device data along with reliability data are comparable with data from devices fabricated by the conventional ex-situ etching process.

Mechanisms in embedded selective epitaxy and overgrowth of an integrated laser/modulator quantum well structure using MOMBE and MOVPE

Lateral integration of optoelectronic devices comprising strained multiple quantum well (MQW) structures can most successfully be accomplished by selective area epitaxy using metal organic molecular beam epitaxy (MOMBE). We optimized the growth parameters with respect to a planar butt coupling and sharp, flat MQW interfaces in an integrated MQW laser / MQW modulator structure. Defect generation in metal organic vapor phase epitaxy (MOVPE) overgrown cladding layers is analyzed and shown to contain information about the quality of the buried butt coupling. A ridge waveguide structure has successfully been fabricated from an optimized integrated laser / modulator structure.