2019年7月23日星期二

A review on MBE-grown HgCdSe infrared materials on GaSb (211)B substrates

We review our recent efforts on developing HgCdSe infrared materials on GaSb substrates via molecular beam epitaxy (MBE) for fabricating next generation infrared detectors with features of lower production cost and larger focal plane array format size. In order to achieve high-quality HgCdSe epilayers, ZnTe buffer layers are grown before growing HgCdSe, and the study of misfit strain in ZnTe buffer layers shows that the thickness of ZnTe buffer layer needs to be below 300 nm in order to minimize the generation of misfit dislocations. The cut-off wavelength/alloy composition of HgCdSe materials can be varied in a wide range by varying the ratio of Se/Cd beam equivalent pressure during the HgCdSe growth. Growth temperature presents significant impact on the material quality of HgCdSe, and lower growth temperature leads to higher material quality for HgCdSe. Typically, long-wave infrared HgCdSe (x=0.18, cut-off wavelength of  at 80 K) presents an electron mobility as high as , a background electron concentration as low as 1.6×1016 cm−3, and a minority carrier lifetime as long as . These values of electron mobility and minority carrier lifetime represent a significant improvement on previous studies of MBE-grown HgCdSe reported in the open literatures, and are comparable to those of counterpart HgCdTe materials grown on lattice-matched CdZnTe substrates. These results indicate that HgCdSe grown at the University of Western Australia, especially long-wave infrared can meet the basic material quality requirements for making high performance infrared detectors although further effort is required to control the background electron concentration to below 1015 cm−3. More importantly, even higher quality HgCdSe materials on GaSb are expected by further optimizing the growth conditions, using higher purity Se source material, and implementing post-growth thermal annealing and defect/impurity gettering/filtering. Our results demonstrate the great potential of HgCdSe infrared materials grown on GaSb substrates for fabricating next generation infrared detectors with features of lower cost and larger array format size.



Source:IOPscience

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2019年7月17日星期三

Investigation of GaSb epilayer grown on vicinal GaAs(001) substrate by high resolution x-ray diffraction

GaSb epilayers grown on GaAs(001) vicinal substrate misoriented towards (111) plane were studied using high-resolution x-ray diffraction (HRXRD). The results show that GaSb epilayers exhibit positive crystallographic tilt and the distribution of 60° misfit dislocations (MDs) is imbalanced. The vicinal substrate also leads to the anisotropy of the mosaic structure, i.e. the lateral coherent lengths in [1\bar 10] directions are larger than those in [110] directions. Furthermore, the full-width at half maximum (FWHM) of the off-axis peaks varies with the inclination angle, which is a result of different dislocation densities in the \{111\} glide planes.



Source:IOPscience

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2019年7月9日星期二

Selective area heteroepitaxy of GaSb on GaAs (001) for in-plane InAs nanowire achievement

The growth of in-plane GaSb nanotemplates on a GaAs (001) substrate is demonstrated combining nanoscale patterning of the substrate and selective area heteroepitaxy. The selective growth of GaSb inside nano-stripe openings in a SiO2 mask layer is achieved at low temperature thanks to the use of an atomic hydrogen flux during the molecular beam epitaxy. These growth conditions promote the spreading of GaSb inside the apertures and lattice mismatch accommodation via the formation of a regular array of misfit dislocations at the interface between GaSb and GaAs. We highlight the impact of the nano-stripe orientation as well as the role of the Sb/Ga flux ratio on the strain relaxation of GaSb along the [110] direction and on the nanowire length along the [1-10] one. Finally we demonstrate how these GaSb nanotemplates can be used as pedestals for subsequent growth of in-plane InAs nanowires.



Source:IOPscience

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2019年7月5日星期五

The growth of n-type GaSb by metal-organic chemical vapour deposition: effects of two-band conduction on carrier concentrations and donor activation

n-type GaSb has been prepared by metal-organic chemical vapour deposition with tellurium donors using diethyltelluride as the dopant precursor. The maximum carrier concentration achieved was 1.7 × 1018 cm−3, as measured by van der Pauw–Hall effect measurements, for an atomic tellurium concentration of 1.8 × 1019 cm−3. The apparent low activation of tellurium donors is explained by a model that considers the effect of electrons occupying both the Γ and L bands in GaSb due to the small energy difference between the Γ and L conduction band minima. The model also accounts for the apparent increase in the carrier concentration determined by van der Pauw–Hall effect measurements at cryogenic temperatures.



Source:IOPscience

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