Insight into precursor kinetics using an infrared gas analyser

Precursor kinetics and its influence on MOCVD growth was investigated using an infrared absorption gas analyser. After several refinements, the analyser was able to be used to measure time dependent concentrations of precursors in the growth zone. Changes were induced by periodic switching of corresponding bubbler valves. It was proved that precursor transport could be accurately described by the combined plug flow and perfectly mixed tank model. The studies of the precursor trans-port are strategically important for the growth of multilayer structures, when growth time of particular layers becomes comparable to delays and time constants. One example is quantum wells or interdiffused multilayer process (IMP) used in the growth of Hg1-xCdxTe heterostructures, where knowledge of precursor transport characteristics is vital for understanding and properly designing that growth. The model parameters, sc. the delays and time constants for DIPTe and DMCd, were evaluated for various growth conditions and then successfully used to optimise the growth of complex Hg1−xCdxTe heterostructures.

Control of acceptor doping in MOCVD HgCdTe epilayers

The acceptor doping of mercury cadmium telluride (HgCdTe) layers grown by MOCVD are investigated. (111)HgCdTe layers were grown on (100)GaAs substrates at 350°C using horizontal reactor and interdiffused multilayer process (IMP). TDMAAs and AsH3 were alternatively used as effective p-type doping precursors. Incorporation and activation rates of arsenic have been studied. Over a wide range of Hg1−xCdxTe compositions (0.17 < x < 0.4), arsenic doping concentration in the range from 5×1015 cm−3 to 5×1017 cm−3 was obtained without postgrowth annealing. The electrical and chemical properties of epitaxial layers are specified by measurements of SIMS profiles, Hall effect and minority carrier lifetimes. It is confirmed that the Auger-7 mechanism has decisive influence on carrier lifetime in p-type HgCdTe epilayers.

Excess Carrier Lifetimes in (HgCd)Te Grown by Mocvd Interdiffused Multilayer Process

Transient lifetime measurements on p- and n-type Hg1−xCdxTe epitaxial films, grown by the MOCVD-interdiffused multilayer process (IMP) on CdTe and CdZnTe, are reported. Lifetimes have been measured on undoped n-type, vacancy and arsenic doped p-type (HgCd)Te for x-values of 0.20–0.28 over the 25K–300K temperature range. Lifetime characterization has been carried out primarily by non-contact transient millimeter wave reflectance as well as by standard photoconductive decay. It is shown that Auger limited lifetimes are achievable in undoped n-type material. N-type lifetime results are analyzed within the framework of a multilevel Shockley-Read model which provide insight into the nature and density of defect states in the material. In p-type (HgCd)Te, for the same carrier concentration, longer lifetimes are obtained by As-doping than in vacancy doped material.

Excess Carrier Lifetimes in (HgCd)Te Grown by Mocvd Interdiftused Multilayer Process

ABSTRACTTransient lifetime measurements on p- and n-type Hg1-xCdxTe epitaxial films, grown by the MOCVD-interdiffused multilayer process (IMP) on CdTe and CdZnTe, are reported. Lifetimes have been measured on undoped n-type, vacancy and arsenic doped p-type (HgCd)Te for x-values of 0.20-0.28 over the 25K-300K temperature range. Lifetime characterization has been carried out primarily by non-contact transient millimeter wave reflectance as well as by standard photoconductive decay. It is shown that Auger limited lifetimes are achievable in undoped n-type material. N-type lifetime results are analyzed within the framework of a multilevel Shockley-Read model which provide insight into the nature and density of defect states in the material. In p-type (HgCd)Te, for the same carrier concentration, longer lifetimes are obtained by As-doping than in vacancy doped material.

Atomic Force Microscopy of Growth Features on Epitaxial CdHgTe Films

ABSTRACTAtomic Force Microscopy has been used to observe the details of surface morphology on CdxHg1-xTe epitaxial films. On films grown by liquid phase epitaxy (LPE), tiered pyramidal features were observed and these are consistent with enhanced nucleation and growth at emergent edge dislocations which thread through from subgrain boundaries in the substrate. On films grown by metal-organic vapour phase epitaxy (MOVPE) using the interdiffused multilayer process (IMP), terraces and steps are observed as expected but the step edges are decorated. It is suggested that this corresponds to the deposition of one binary layer in Volmer-Weber mode.