Naoya Miyoshi

Growth of Large GaN Single Crystals on High-Quality GaN Seed by Carbon-Added Na Flux Method

Seeded growth on high-quality GaN seed was studied using a carbon-added Na flux method. A GaN single crystal (8.6 mm long, 5 mm high) was grown in 96 h without polycrystal formation on a crucible. Under a carbon-added condition, dependence of the growth rate of the seed and the growth habit on the flux composition was studied. We found that the growth rate was higher with Ga-poor flux, resulting in a high growth rate of 30 µm/h along the c-axis and 33 µm/h along the a-axis (66 µm/h for both sides). The growth habit changed from prismatic to pyramidal with increasing Ga composition.

Growth of GaN single crystals by a Ca- and Ba-added Na flux method

GaN substrates are desirable for fabricating ultra-violet LEDs and LDs, and high-power and high-frequency transistors. High-quality GaN single crystals can be obtained by using Na flux method, but the growth habit of bulk crystals must be controlled. In this study, we investigated the effects of additives (Ca, Ba) on the growth habit and impurity concentration in the crystals. The aspect ratio (c/a) of the crystals was increased by increasing the amount of additives, showing that the growth habit could be changed from the pyramidal shape to the prism shape. Ba concentration was below the detection limit (1x1015 atoms/cm3).

LPE Growth of Bulk GaN Crystal by Alkali-Metal Flux Method

We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the Na flux method. Our success is due to the development of a new apparatus for growing large GaN single crystals. The crystal grown in this study has a low dislocation density of 2.3×105 (cm-2), The secondary ion mass spectrometry (SIMS) technique demonstrates that the Na element is difficult to be taken in the crystal in both the + and – c directions, resulting in a Na concentration of 4.2 × 1014 (cm-3) in the crystal. Our success in growing a two-inch GaN substrate with a low impurity content and low dislocation density should pave the way for the Na flux method to become a practical application.