This article describes the edge-defined film-fed growth (EFG) process of β-Ga2O3 bulk crystals. We first describe the conditions of the bulk crystal's growth and the fabrication process of the wafers. Then, we discuss the efforts to control electrical properties, and give some experimental results of residual impurity measurement, intentional doping using Si and Sn for n-type doping and Fe for insulating doping, and the effects of annealing on donor concentration. We also discuss recent findings on β-Ga2O3 bulk crystals' main crystal defects.
A new approach to β-Ga2O3 single crystal growth was studied using a directional solidification process in a vertical Bridgman furnace in ambient air. The crucibles used were made of platinum-rhodium alloy as they are capable of withstanding high temperatures that exceed the melting temperature of β-Ga2O3 in ambient air.
We succeeded in growing 1-inch diameter β-Ga2O3 single crystals with a growth direction perpendicular to an (100) faceted plane without a seed crystal. We have also grown β-Ga2O3 single crystals from seed crystals cut from the single crystals previously grown without seed crystals. It was found that β-Ga2O3 single crystals could be grown in platinum-rhodium alloy crucibles in ambient air, with no adhesion of the crystal to the crucible wall. Thus, we confirmed that our new approach could be useful for growing β-Ga2O3 single crystals.
We have investigated defects in beta-type gallium oxide (β-Ga2O3) single crystals by X-ray topography, selective etching, and transmission electron microscopy. Two types of defects, namely, dislocations and nanopipes, were found. Dislocations are screw dislocations with Burgers vector parallel to . Nanopipes are hollow slits having rod-like cross section and elongated along .
Three types of defects in β-Ga2O3 crystals grown by edge-defined film-fed growth process have been characterized by transmission electron microscopy, focused ion beam scanning ion microscopy, and related techniques. First, arrays of edge dislocations were observed corresponding to etch pit arrays on a (201)-oriented wafer after etching with hot H3PO4. In some of the dislocations, the line-shaped appearance is slightly deformed due to an inhomogeneous strain field. Next, platelike nanovoids which correspond to etch pits on the (010) plane were observed. Although the crystallographic configurations of the defects are different from that of nanometer-sized crystalline grooves which have been previously reported, they are both classified as similar type of nanovoids. Finally, twin lamellae as well as regular large twins were observed in the crystal. The twin lamellae correspond to shallow V-grooves revealed after the chemical etching.
β-gallium oxide is very promising for power device semiconductor. We specify the type and character, such as dislocation and void. Next, we fabricate and measure Shottky barrier diodes (SBD) on the entire surface and investigate a relation between its leakage current and defects revealed mainly by etchpit method. It is found that the dislocations appeared on the (010) become SBD leakage path, but the dislocations on the (201) and (001) surfaces seem to have no relation with the SBD leakage current. Then, it seems that voids appeared on all surface orientations do not affect the SBD leakage current.