E. Richter

Carbon doping for the GaAs base layer of Heterojunction Bipolar Transistors in a production scale MOVPE reactor

In this work different approaches for carbon doping of GaAs in MOVPE are compared with respect to their growth-and device-related material properties. Doping levels up to 6 x 10 19 cm -3 and smooth surface morphologies are achieved with either intrinsically (TMG and AsH 3 or TMAs) or extrinsically (CBr 4 ) doped layers. Despite comparable structural and majority carrier properties differences in GaInP/GaAs-HBT device performance depending on base doping conditions are obtained. Devices with an intrinsically doped base layer (TMG + AsH 3 ) show superior transistor performance with a current gain to base sheet resistance ratio (β/R sb ) exceeding 0.5 for base thicknesses as large as 120 nm. The use of either CBr 4 or TMAs as base growth precursors results in reduced current gains (β/R sb ≤ 0.3). It is shown that the achieved HBT current gain is directly related to recombination centers in the heavily doped base layer depending on doping method.

GaN substrates by HVPE

The availability of GaN substrates is crucial for GaN-based laser diodes. Also high performance LEDs ask for high quality substrates. Methods for growth of bulk GaN are reviewed with a focus on hydride vapour phase epitaxy (HVPE), which currently is the method used for the production of GaN substrates. Also the ammonothermal approach is briefly discussed. Both approaches still have to overcome limitations before mass-production at affordable prices is feasible. These limitations are related to the maximum growth rate yielding high quality material as well as the boule length that can be achieved together with high material quality.

Carbon doped GaAs grown in low pressure-metalorganic vapor phase epitaxy using carbon tetrabromide

Carbon tetrabromide was used as carbon source for heavily p-doped GaAs in low pressure metalorganic vapor phase epitaxy (MOVPE). The efficiency of carbon incorporation was investigated at temperatures between 550 and 670°C, at V/III ratios from 1 to 50 and carbon tetrabromide partial pressures from 0.01 to 0.03 Pa. Hole concentrations from 8 × 1017 to 5 × 1019 cm−3 in as-grown layers were obtained. After annealing in nitrogen atmosphere at 450°C, a maximum hole concentration of 9 × 1019 cm−3 and a mobility of 87 cm2/Vs was found. At growth temperatures below 600°C, traces of bromine were detected in the layers. Photoluminescence mapping revealed an excellent doping homogeneity. Thus, CBr4 is found to be a suitable carbon dopant source in MOVPE.

Direct Growth of GaN on (0001) Sapphire by Low Pressure Hydride Vapour Phase Epitaxy

A two-step process for GaN on (0001) sapphire based on low-temperature GaN nucleation in low pressure hydride vapour phase epitaxy using a conventional reactor is described. The process allows reproducibly for subsequent growth of high-quality GaN layers eliminating the need for ex-situ pregrowth processes like sputtering of ZnO or use of MOVPE-grown templates. By means of electron microscopy and thin film X-ray diffraction it is shown that the nucleation procedure yields high-density nucleation centers of the same orientation as the substrate and promotes the lateral growth of epitaxial GaN films.

Effects of storage time of epi-ready InP:Fe substrates on the quality of metalorganic vapour phase epitaxial grown InP

Abstract InP layers have been grown on epi-ready InP:Fe substrates by metalorganic vapour phase epitaxy (MOVPE). Hall measurements show an influence of the storage time of wafers on the electrical properties of the grown epitaxial layers. Hall data and electrochemical capacitance-voltage (ECV) profiles document an increase of donors at the substrate-epilayer interface for longer storage times. They also point to the existence of deep donors at the interface. The concentration of deep donors can be associated with the high oxygen level at the interface detected by secondary ion mass spectroscopy (SIMS). Ellipsometry proves that the oxide layer grows in thickness with time. Even after only four months of storage it was not possible to completely remove this oxide layer by thermal annealing under phospine.

Hydride Vapor-Phase Epitaxy of c-Plane AlGaN Layers on Patterned Sapphire Substrates

Growth of AlxGa1−xN layers by hydride vapor-phase epitaxy on patterned sapphire substrates is investigated. The pattern consists of honeycombs which by their orientation and size promote the formation of coalesced c-plane-oriented AlxGa1−xN layers with reduced crack density. The orientation of parasitic crystallites in the honeycomb openings is investigated using scanning electron microscopy and electron back-scatter diffraction. Crystallites with their [

Structure investigations of nonpolar GaN layers

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Critical issues of growth optimization for Ga0.5In0.5P/GaAs heterojunction bipolar transistors

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