Kah Pin Chen

Heteroepitaxial growth of GaAs on (100) Ge/Si using migration enhanced epitaxy

In this paper, heteroepitaxial growth of GaAs on nominal (100) Ge/Si substrate was investigated. The root-mean square surface roughness of the sample where the first few monolayers of the GaAs were nucleated by migration enhanced epitaxy (MEE) is four times smaller compared to the sample without such a process, indicating better surface planarity. From the (004) x-ray diffraction rocking curve measurement, the full width at half maximum of the GaAs layer nucleated by MEE is 40% lower compared to that of the GaAs layer without such a process, indicating better crystal quality. Furthermore, it was found that the sample where the GaAs layer was nucleated by MEE experienced early relaxation. As the MEE process promotes two-dimensional growth, the GaAs layer where nucleation was initiated by such a process has fewer islandlike formations. This leads to a pseudomorphically grown GaAs layer, which experiences higher strain compared to the GaAs layer with more islandlike formations, where most relaxation occurs o...

Study of surface microstructure origin and evolution for GaAs grown on Ge/Si1−xGex/Si substrate

The origin and evolution of surface microstructures in the GaAs layer grown on the Ge/Si1−xGex/Si substrate were studied. The characteristic surface microstructures are formed in pairs. By correlating the results from atomic force microscopy and cross-sectional transmission electron microscopy characterization, these paired surface microstructures are identified as { 111 } stacking faults that propagate at 54 ◦ with respect to the substrate surface. The stacking faults originate from the single-stepped GaAs/Ge heterointerface, as a consequence of in situ annealing of the Ge surface. The surface microstructure density becomes lower and the mean lateral size larger when the GaAs thickness is increased from 0.54 to 1.11 µm. (Some figures in this article are in colour only in the electronic version)

Characterization of carbon-doped InSb diode grown by molecular beam epitaxy

Carbon-doped p-type InSb layers grown by solid source molecular beam epitaxy are characterized using a p+–n diode structure. Based on the combination of current–voltage, secondary ion mass spectroscopy and x-ray diffraction measurements, carbon is proven to be an effective p-type dopant for InSb with hole concentration reaching the range of 1019 cm−3. It is also proven that the use of the Hall effect to determine the hole concentration in the p-type InSb layer may be unreliable in cases where the leakage current in the p+–n junction is high. A thermal trap-assisted tunnelling model with two trap levels successfully explains the origin of leakage current mechanisms in the carbon-doped InSb samples. Good agreement between measured and calculated dc characteristics of the diodes at reverse bias up to −3 V from 30 to 120 K supports the validity of the current transport model.

Characterization of GaAs grown on SiGe/Si graded substrates using p-n junction diodes

The effect of GaAs buffer thickness on the electrical characteristics of a p+-n− junction diode is presented. The GaAs diodes are grown on a Ge/graded SixGe1−x/Si virtual substrate. Electrical characterization and visual observation provided vital insights into the origin of improvement in the electrical characteristics of the diode as the GaAs buffer thickness is increased. A high breakdown voltage of −9.2 V was achieved as the buffer thickness was increased from 50 to 600 nm, as the ideality factor reduces from 2.2 to 1.7, indicating reduction in the recombination current in the depletion region. This improvement is found to be related to the suppression mechanism of the wedge-shaped dislocation formation in the growth direction. This evidence provides important insights for the integration of III-V semiconductor devices, such as heterojunction bipolar transistor, with Si-based substrates.

1EV GAN x AS 1-x-y SB y material for lattice-matched III–V solar cell implementation on GaAs and Ge

The effect of different arsenic species (As<inf>2</inf> or As<inf>4</inf>) on the quality of molecular beam epitaxy (MBE) grown GaNAsSb materials (samples A and B) and GaAs/ GaNAsSb/GaAs p⁺ n⁻ n⁺ devices (samples C and D) were investigated. The improvement in material quality in sample B, as well as the improvement in diode and solar cell characteristics in sample C, may suggest a successful defect density manipulation using As<inf>2</inf> overpressure for GaNAsSb growth.