Yih-Der Guo

Study of twins in GaAs, GaP and InAs crystals

Abstract Twins in three different III–V compound semiconductors, including GaAs, GaP, and InAs, crystals have been studied by both chemical etching method and transmission electron microscopy. From chemical etching it is concluded that the growth conditions which result in the generation of large irregular facets also favor the formation of twins. However, the facets are not necessarily the nucleation sites of twins. All twins in III–V compound semiconductors are identified by chemical etching method to be 60° rotation twins.

Characteristics of facets in Si-doped GaAs crystals grown by horizontal Bridgman technique

Abstract Dislocation free Si-doped GaAs crystals, 2 inches in diameter, 30 cm in length and carrier concentration of 1018 cm-3, have been growm by horizontal Bridgman (HB) technique. Large facets were found to be more prone to form under a longitudinal temperature gradient less than 1°C/cm. Characteristics of facets in these HB grown GaAs crystals have been investigated. The occurence of large facets resulted in the lifting of the top surface of the crystal. Facets were found to be more prone to form by reducing the temperature gradient, increasing the Si-dopant concentration and the growth rate. Perpendicular twins, which were related to the (1, 1, 1) facet growth, were generated at the positions where the facet size varied drastically. These twins were identified to be 60° rotation twins by chemical etching method. The carrier concentration of the facet area, as measured by Van der Pauw and spreading resistance methods, was found to be 1.7–2.0 times higher than that of the non-facet area. The dislocations in the non-facet area were observed to terminate at the boundary of facet and non-facet areas.

A modified horizontal Bridgman technique without arsenic zone for growth of GaAs crystals

Abstract A modified two temperature zone horizontal Bridgman system without arsenic zone has been developed for the growth of GaAs single crystal. In this process, a short quartz ampoule, which was just long enough for sealing off the boat, was used. With a short quartz ampoule and a large charge of polycrystalline GaAs, the arsenic loss due to the dissociation of the melt was very small. The sticking between the boat and the crystal was eliminated; therefore, the crystal yield was greatly enhanced. The possible reasons for the elimination of the boat sticking and the stoichiometry control in this process are discussed. High quality Si-doped GaAs crystals with 2 inches in diameter and 30 cm in length have been routinely grown. The optoelectronic devices fabricated with these wafers showed better performance than commercial products.

Influence of through-window radiation on the horizontal Bridgman process for rectangular shaped GaAs crystals

Abstract Si-doped GaAs crystals with a rectangular cross section have been grown using the modified two-temperature horizontal Bridgman (M2T-HB) technique [1]. A viewing window was opened on top of the furnace to monitor the growth process of rectangular GaAs crystals. By controlling the position and shape of the solid/liquid interface underneath the viewing window, lineage defects were eliminated and crystals of low dislocation density were successfully grown. Numerical analysis based on a semi-implicit finite difference scheme was performed with a radiative boundary condition imposed on the surface of solid crystal. The effect of radiative heat loss through the viewing window is discussed.

The growth and characterization of GaAs single crystal by a modified horizontal bridgman system

Abstract A modified two-temperature zone horizontal Bridgman (M2T-HB) system to grow high quality GaAs crystals is described in detail. GaAs crystals of 2 inch diameter and 30 cm length can be routinely grown by the M2T-HB technique. Keeping the solid/melt interface flat with the specially designed liner construction and viewing window, as well as eliminating the sticking between the quartz boat and GaAs crystals, lineage defects can be eliminated and the dislocation density can be greatly reduced. Moderately Si-doped GaAs crystals have etch pit densities (EPDs) lower than 2000 cm -2 . For moderately Si-doped GaAs crystals, the best result shows that EPDs are lower than 700 cm -2 in the whole ingot. Nearly dislocation free Si-doped GaAs crystals with high carrier concentration of (1−4)×10 18 cm -3 can also be grown by this technique. Zn-doped GaAs crystals with carrier concentration in the range of (1−5)×10 19 cm -3 have EPD lower than 3000 cm -2 . The carrier concentrations of undoped GaAs crystals are in the range of (5−10)×10 15 cm -3 . The result indicated that high purity GaAs crystals with low Si contamination can be grown by M2T-HB technique.

Bevelled-sidewalls formation and its effect on the light output of GaInN MQW LED chips

In this research, experiments and optical simulations have been carried out to study the effect of bevelled sidewalls and geometric shapes on the light extraction efficiency of GaN LED chips. Besides the conventional rectangular chips, hexagonal LED chips were experimentally processed for the fist time on a novel island-like GaN substrate. The bevelled sidewalls could be naturally formed on the chips during the growth of GaN islands by HVPE technology. The results of simulations and experiments are consistent with each other, and show that the output power of LED will be improved doubly when the sidewalls were beveled on the chip. The light output from hexagonal LED chips is also proved better than that from conventional rectangular chips.