Floral design GaN crystals: low-resistive and low-dislocation-density growth by oxide vapor phase epitaxy

Abstract

GaN crystal growth mode in the oxide vapor phase epitaxy (OVPE) method, which simultaneously provides low electrical resistance and low threading dislocation density (TDD), has been investigated in detail. The results clarified that these qualities can be achieved by the expression of numerous inverted pyramidal pits, called three-dimensional (3D) growth mode. This mode reduced TDD from 3.8 × 106 cm−2 to 2.0 × 104 cm−2 for 1 mm thick growth because the threading dislocations (TDs) converged to the center of each pit. Moreover, when the crystal surface after polishing was observed by photoluminescence measurement, peculiar floral designs reflecting the distribution of oxygen concentration were observed over the entire surface. In addition, the etch pits exhibited TDs in the center of each floral design. On the basis of our results, we proposed that the 3D-OVPE-GaN will serve as a key material for improving the performance of vertical GaN devices.

High-rate OVPE-GaN crystal growth at a very high temperature of 1300 °C

“…If we defined the dopant activation ratio as carrier concentration/oxygen concentration, it was estimated to be 38%. In the previous study, the dopant activation ratio of 3D-OVPE-GaN crystal was 15%, 17) suggesting that the dopant activation ratio was improved by increasing the growth temperature. Since the carrier concentration increased sublinearly to the oxygen concentration (shown in Fig.…”

“…The surface morphology was typical of the 3D-OVPE-GaN crystal. 17) From the cross-sectional SEM image in Fig. 2(b), there were no voids at the interface between the seed substrate and the epi-layer.…”

“…15,16) Furthermore, due to the growth mode of OVPE-GaN, which consists of faceted surfaces, dislocations are bent and promoted to coalesce or annihilate each other, resulting in low threading dislocation density (TDD). 17) Therefore, OVPE-GaN crystal has the potential for producing low cost, low resistivity, and low TDD GaN substrates and is expected to play a major role in popularizing GaN power devices.…”

“…The TDD of OVPE-GaN crystal can be estimated from not only the etch pit density but also the pit density of an as-grown crystal, the so-called "growth pit" density. 17) The larger the growth pit size during the crystal growth is, the lower the TDD after the growth is. Under the growth condition in this study, larger growth pits were not produced, hence there was a less effective reduction of threading dislocations.…”

Elastic constants of GaN grown by the oxide vapor phase epitaxy method

“…The oxide vapor phase epitaxy (OVPE) method is promising because it is capable of realizing thick single crystals without producing solid byproducts. [3][4][5][6] The OVPE GaN has the unique characteristic of allowing very high oxygen impurities, leading to low resistivity and optically black crystal color. Oxygen is a common impurity in GaN, and it acts as a donor.…”