H. C. Kuo

Activation studies of low-dose Si implants in gallium nitride

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose ∼5×1014 cm−2. Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at 1150 °C in N2 for 5 min. exhibited a smooth surface morphology and a sheet electron concentration ns∼6.8×1013 cm−2.

Be diffusion in InGaAs/InP heterojunction bipolar transistors

Classic signatures of Be diffusion were observed in InAlAs/InGaAs HBTs after elevated temperature bias stress, i.e., a positive shift in the Gummel plot, higher collector ideality, and higher offset voltage. An activation energy of 1.57 eV was calculated. Lifetimes of 3.3/spl times/106 h and 37000 h were extrapolated for low and high power operation, respectively. In contrast, an InP/InGaAs HBT with a C doped base showed no signatures of C diffusion. The results show that Be diffusion is manageable at lower power. They also support the idea that C is more stable than Be in this material system.

p‐type InGaAs/InP quantum well infrared photodetector with peak response at 4.55 μm

Lattice‐matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p‐type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n‐type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data.

Precipitate formation in carbon-doped base of InGaP/GaAs heterojunction bipolar transistors grown by low-pressure metal organic chemical vapor deposition

The effect of intermediate temperature annealing on the carbon-doped base region of InGaP/GaAs heterojunction bipolar transistors (HBTs) was studied. This work shows that after annealing at only 600 °C a sample doped at 5.5×1019 cm−3 displays carbon precipitation. InGaP/GaAs HBT structures were grown for the annealing study. Hall measurements were used to measure hole concentration. Atomic force microscopy was employed to identify carbon precipitation. The annealing process not only removes hydrogen from the base but also creates carbon precipitates. The dc current gain measurements imply that the carbon precipitates increase base recombination. These results are very important in the growth and postgrowth annealing of high gain HBTs.

Optical and structural characterization of InAsP/InGaP strain compensated multiple quantum wells grown by GSMBE

High-quality InAsP/InP (3ML)/InGaP SC-MQWs with zero net strain up to 40 periods were grown by GSMBE. Compared with uncompensated InAsP/InP strained MQWs and InAsP/lnGaP SC-MQWs without the InP insertion layers, much sharper and symmetric satellite peaks in double-crystal X-ray diffraction and excellent photoluminescence was obtained from SC-MQWs with the InP insertion layers.

Comparison of intersubband GaAs/AlGaAs multiple quantum well infrared photodetectors on GaAs and GaAs-on-Si substrates

We have successfully fabricated intersubband GaAs/AlGaAs quantum well infrared photodetectors grown on GaAs-on-Si substrate and evaluated their structural, electrical, and optical characteristics. We have found that the performance is comparable to a similar detector structure grown on a semi- insulating GaAs substrate. The results are promising for applications in the important 8 - 12 micrometer atmospheric window.

Intermixed quantum well photodetectors for long-wavelength detection

Intermixing of the well and barrier layers in quantum well infrared photodetectors (QWIPs) can be used to realize a broadened spectral response as well as multiple color detectors. We describe die experimental results of both rapid thermal annealing (RTA) and laser annealing (LA) QWIPs operating in the 8-12µm regime. The peak spectral response of the annealed detectors was shifted to longer wavelength as compared to die as-grown detectors. In general, a decrease in detector performance after annealing is also observed which may be attributable to a change in the absorption coefficient caused by the out-diffiision of dopants during annealing. Recent advances in growth technology, complimented by innovative structures should offset any degredation in performance. Thus, the post-growth control of the composition profiles by annealing offers opportunities to fine tune various aspects of a QWIP’s response.

Effect of gas switching on InP/InGaAs interfaces during CBE growth

In this paper, the effect of a simple gas switching sequence on interface abruptness during CBE growth is studied using double crystal X-ray diffraction (DCXRD), photoluminescence (PL), and scanning tunneling microscopy (STM). Optimization of the switching sequence produces monolayer abruptness for both the InP/InGaAs and the InGaAs/InP interfaces.