Study on bulk crystal growth for nitide semiconductors

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GaN-based devices such as InGaN/GaN blue LEDs have been fabricated with sapphire substrates. High density of dislocations due to the large lattice mismatch between growing layers and the substrate are known to cause the limited performances and low reliability of such devices. The motivation of this study is to provide III-nitride bulk crystals which can be used for homoepitaxial growth of nitride films. The study is focused on the nitridation of III-arsenide or -phosphide bulk crystals such as GaAs or GaP in a flowing ammonia in order to convert them into III-nitide bulk crystals. Results are summarized as follows..1) Nitridation behavior of III-arsenides and -phosphides: XPS analysis reveals that GaN + AsNィイD2xィエD2 and metallic In + AsNィイD2xィエD2 are formed after the nitridation of GaAs and InAs, respectively, while GaN + PNィイD2xィエD2 after the nitridation of GaP and InP, respectively. Due to the thermal instability of AsNx, only GaN is obtained after the nitridation of GaAs at a tempe … More rature higher than 550℃. The thermal stability of PNx results in the formation of mixture of GaN + PNィイD2xィエD2 after the nitridation even at 900℃. Thus, GaAs is suitable for the formation of bulk GaN by the nitridation.2) Nitridation of GaAs(100) and (111) wafers: When GaAs(100) wafer is nitrided, zincblende GaN crystal is formed with a small fraction of wurtzite GaN crystal. The suppression of wurtzite GaN growth is intensively studied. But it is difficult because of the increasing growth rate of wurtzite GaN as The nitridation proceeds. Wurtzite GaN of single phase is obtained after the nitridation of GaAs(111) wafers. In this case, however, a lump of GaN is composed of thin and porous plate-like crystals, which seems to be difficult to be used as substrates for device fabrication.3) GaN growth by the Synthesis, Solute Diffusion (SSD) method: As a new method for GaN bulk growth, SSD method is also studied. This method was applied for GaP and InP bulk crystal growth. After the growth using metallic Ga and ammonia at 1000℃, wurizite GaN crystals of about 1x 1x 1 mmィイD13ィエD1 size are obtained. Less