Wan Khai Loke

Comparison of nitrogen compositions in the as-grown GaNxAs1−x on GaAs measured by high-resolution x-ray diffraction and secondary-ion mass spectroscopy

High-resolution x-ray diffraction (HRXRD) and secondary-ion mass spectroscopy were used to measure the N compositions of a series of as-grown GaNAs samples grown by solid-source molecular-beam epitaxy. We found that N compositions measured by the two methods agree well at lower N compositions (x 3%). The HRXRD measurement by using Vegard’s law to extract the lattice constant of GaNAs, underestimates N composition at larger N compositions. We found that the underestimation is up to 14.3% at the x=4.2%. In order to explain the deviation, a model for analyzing the correlation between lattice parameters and point defects in the epilayer was carried out.

Growth of GaAs on vicinal Ge surface using low-temperature migration-enhanced epitaxy

In this article, we demonstrate the influence of substrate temperature during migration-enhanced epitaxy (MEE) process of GaAs epitaxy on a vicinal surface of Ge (100), 6° offcut towards the (111) plane. It was found that the offcut surface is not the sufficient condition for suppressing the formation of antiphase domains at the GaAs∕Ge interface. Rather, it has to be complemented by low substrate temperature during the MEE process. GaAs grown at 250°C, the lowest temperature among all the samples, exhibits the smoothest surface and best structural and optical qualities, as characterized by atomic force microscopy, cross-sectional transmission electron microscopy, and low-temperature photoluminescence, respectively. At this substrate temperature, As dimers are adsorbed onto the substrate surface more readily with negligible reevaporation, ensuring complete coverage on the Ge surface with double-atomic steps. Complete coverage by As proved to be crucial in preventing the occurrence of inversion boundaries,...

Photoluminescence characteristics of GaInNAs quantum wells annealed at high temperature

The photoluminescence (PL) characteristics of GaInNAs quantum wells (QWs) after high-temperature postgrowth annealing were studied. The QWs were grown using a radio-frequency nitrogen plasma source in conjunction with a solid-source molecular-beam epitaxy system. It was found that annealing at high temperature (840 °C) and long duration (10 min) results in significant improvements to the PL characteristics of the GaInNAs QWs. The shift of the GaInNAs and GaInAs PL peak wavelength resulting from high-temperature annealing is dependent on the In composition. It is suggested that the dominant mechanisms that give rise to the blueshift of the PL peak wavelength in GaInNAs QWs with high-In composition are residual-strain-induced GaAs/GaInNAs/GaAs interface interdiffusion, and defect-assisted diffusion-related effects, both of which originate from the growth process.

High-speed picosecond pulse response GaNAsSb p-i-n photodetectors grown by rf plasma-assisted nitrogen molecular beam epitaxy

The authors report on picosecond pulse response GaNAsSb∕GaAs p-i-n photodetectors grown by molecular beam epitaxy in conjunction with a rf plasma-assisted nitrogen source. The 2μm thick GaNAsSb photoabsorption layer contains 3.3% of N and 8% of Sb resulting in a dc photoresponse up to 1380nm wavelength. Dark current densities at 0 and −5V are 1.6×10−5 and 13A∕cm2, respectively. The GaNAsSb photodiodes exhibit a record pulse response width of only 40.5ps (full width at half maximum) corresponding to a 4.5GHz bandwidth.

Germanium-Tin on Si Avalanche Photodiode: Device Design and Technology Demonstration

We report the demonstration of a Ge_0.95Sn_0.05 on silicon (Ge_0.95Sn_0.05/Si) avalanche photodiode (APD) having a separate-absorption-charge-multiplication structure, wherein a Ge_0.95Sn_0.05 layer and a Si layer function as an absorption layer and a multiplication layer, respectively. Material characterization was performed by atomic force microscopy, X-ray diffraction, and transmission electron microscopy. The dark current I_dark of the APD is dominated by the area-dependent bulk leakage rather than the surface leakage. The temperature dependence of breakdown voltage of the Ge_0.95Sn_0.05/Si APD was characterized and a thermal coefficient of 0.05% K^-1 was obtained, achieving a lower thermal sensitivity than the conventional III-V-based APDs. In the wavelength range of 1600-1630 nm, a responsivity of ~1 A/W (bias voltage V_bias = -9.8 V) was achieved due to the internal avalanche gain.

Characterization of small-mismatch GaAsSbN on GaAs grown by solid source molecular beam epitaxy

GaAsSbN layers with small lattice mismatch to GaAs were studied for possible application as the intrinsic layer in a GaAs-based p‐i‐n photodetector. Our calculation has shown that small lattice mismatch GaAsSbN to GaAs could be achieved at an Sb∕N atomic ratio of 2.60. GaAsSbN was grown as the intrinsic layer for a GaAs∕GaAsSbN∕GaAs photodetector structure using solid-source molecular beam epitaxy in conjunction with a radio frequency (rf) plasma-assisted nitrogen source and valved antimony cracker source. The lattice mismatch of the GaAsSbN layer to GaAs was kept below 5000ppm, which is sufficient to maintain coherent growth of ∼0.5μm thick GaAsSbN on GaAs substrate. The growth temperature was varied between 420 and 520°C, and the Sb flux beam equivalent pressure between 1.7×10−8 and 2.3×10−8Torr to maintain coherent growth. All samples exhibit room temperature photocurrent response in the 1.3μm wavelength region. X-ray diffraction two-dimensional maps showed diffuse scattering, which may have been cause...

Electroluminescence and structural characteristics of InAs/In0.1Ga0.9As quantum dots grown on graded Si1−xGex/Si substrate

We studied the electroluminescence and structural characteristics of five-layer stacked self-assembled InAs/In0.1Ga0.9As quantum dot (QD) structures grown on graded Si1−xGex/Si substrate. The QD was found to take on a lens shaped structure with aspect ratio of 0.23±0.05. Room-temperature electroluminescence at 1.29 μm was observed from the QD structures. The external quantum efficiency as function of injected current was investigated and the dominant carrier recombination processes were identified from analysis of the current-optical power relationship.

Dry Etched Waveguide Laser Diode on GeOI

We demonstrate a top-top contact, dry etched mirror facet III-V waveguide laser diode grown on germanium-on-insulator (GeOI). A 3 × InGaAs/GaAs quantum well designed to lase at 985 nm was grown on a GaAs buffer, which was lattice matched to the GeOI platform in order to realize the monolithic integration of III-V electronic and photonic devices with silicon and SiO2. Lasing occurred at ~ 985 nm with a threshold current density of ~ 2 kA/cm2. Pulsed measurements, and SEM and TEM characterization methods were used. The issue of heat transfer limited the performance of the laser.

Physical device modeling of carbon nanotube/GaAs photovoltaic cells

Photovoltaic response from semiconducting single-walled carbon nanotubes/n-type GaAs heterojunctions has been investigated. We propose a detailed device model of the photovoltaic cell, in which electron transport can be described as follows. The thermionic emission and tunneling through the spike barrier caused by the conduction band discontinuity dominate electron transport under a low and high-forward bias, respectively. In contrast, the dominant transport mechanisms at low and high-reverse bias could be attributed to the direct and Fowler–Nordheim tunneling though a molecular junction, respectively. Within this framework, the current-voltage characteristics of the photovoltaic response can be quantitatively described.

GaAs-based heterojunction p-i-n photodetectors using pentanary InGaAsNSb as the intrinsic layer

GaAs-based double-heterojunction p-i-n photodetectors using In/sub z/Ga/sub 1-z/As/sub 1-x-y/N/sub x/Sb/sub y/ in the i layer is fabricated for the first time using the solid source molecular beam epitaxy growth method. The surfactant effect generated by the presence of Sb in this material allows thick high-quality dilute nitride material growth. A peak responsivity of /spl sim/0.29 A/W, corresponding to quantum efficiencies of 38% is attained between 0.9 and 1.1 /spl mu/m from the best p-i-n device. The cutoff wavelength reaches /spl sim/1.4 /spl mu/m and the dark current is /spl sim/0.43 mA/cm/sup 2/ at a reverse bias of 2 V. A Sb-free p-i-n device consisting of InGaAsN-GaAs is also fabricated to compare the device performance with the InGaAsNSb-GaAs p-i-n devices.