Hydrogenated amorphous silicon germanium alloys (a-SiGe:H) have been prepared by rf glow discharge of silane, germane, and hydrogen gas mixture at substrate temperature of 200 and 250 °C. The structural properties of the films have been investigated by infrared, Raman, and secondary ion mass spectroscopy. It is found that there is a preferential incorporation of germanium into the film relative to silicon and the films with high germane gas phase composition Xg>0.4 tend to oxidize in atmosphere. Besides, polysilane is enhanced in the films with low germane gas phase composition. The electrical properties including dark, photo conductivities, and conduction activation energy are measured. As for the optical properties, optical transmission is adopted to determine the optical gap while photoluminescence spectra together with temperature variation are used to study the band tail states of the films. By applying Brodsky’s quantum well model, the various optical and electrical properties could be explained successfully.

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been fabricated by plasma-enhanced chemical vapor deposition at temperatures ranging from 50 to 250 °C. It is found that as soon as the samples are taken out from the reaction chamber and exposed to the atmosphere, the a-SiNx:H films start to oxide. The oxidation processes are monitored using infrared absorption spectroscopy. A model of porous ‘‘fractal-like network’’ structure, which is probably inherent in low-temperature deposition, is proposed to explain why moisture (H2O) in the air can percolate through numerous microvoids into these films. The H2O molecules which percolate into these porous films are active to react with the —Si—N—Si—, —Si—N—H, and —N—Si—-H bonds and to form more chemically stabilized —Si—O—Si—, —Si—O—H, and H—O—H bond configurations with the result of eventual oxidization of the entire nitride films.

The infrared-absorption spectra of silicon dioxide have been studied for many years and most of the peaks have been identified. During the investigation of silicon dioxide deposited by the liquid-phase-deposition technique, an interesting phenomenon was observed. It was found that the intensity ratio between the side lobe (1200 cm−1) and main peak (1090 cm−1) varies and depends on both the concentration of boric acid and the dilution ratio of the growth solution. Measurement of the refractive index shows that the material with larger absorption at 1200 cm−1 has a smaller index and thus more porous structure; therefore, the peak at 1200 cm−1 is suggested to arise from porous oxide, i.e., Si—O—Si, in a large void.

Amorphous silicon-carbon hydrogen alloy was prepared by radio frequency glow discharge decomposition of a silane-methane mixture. The infrared absorption spectra were measured at various stages of thermal annealing. By observing the change of relative intensities between these peaks the hydrogen bonding responsible for the absorption peaks could be assigned more accurately, for example, the stretching mode of monohydride Si–H is determined by its local environment, which supports H. Wagner’s and W. Beyer’s results [Solid State Commun. 48, 585 (1983)] but is inconsistent with the commonly believed view. It is also found that a significant fraction of carbon atoms are introduced into the film in –CH3 configuration which forms a local void and enhances the formation of polysilane chain and dangling bond defects. Only after high-temperature annealing are the hydrogen atoms driven out, and Si and C start to form a better silicon carbide network.

A 10-stacked InAs/GaAs quantum dot infrared photodetector (QDIP) is compared with a 20-period GaAs/(AlGa)As superlattice infrared photodetector (SLIP). The 2-10 µm wide detection window and 187 mA/W high peak responsivity of InAs/GaAs QDIP at 7 µm at an applied voltage of 1.1 V are superior to the 7-10 µm detection window and 140 mA/W responsivity of GaAs/(AlGa)As SLIP at 9.4 µm at an applied voltage of 1.3 V. The photocurrent of SLIP is temperature-independent, whereas the photocurrent of QDIP increases with increasing temperature from 20 to 100 K. The polarization-dependent response ratios of 0.22 and 0.39 are observed for SLIP and QDIP, respectively.