氮化镓籽晶的表面损伤处理及氨热生长研究

Study on Surface Damage Treatment of GaN Seed and Ammonothermal Growth

籽晶的表面损伤会导致后续生长的晶体位错增多。为了降低籽晶表面的损伤,通常采用粗磨-精磨-抛光的多步过程处理的晶片作为籽晶,工艺步骤多、复杂,成本高。本文采用磷酸去除表面损伤层的粗磨GaN与化学机械抛光的GaN分别作为籽晶,对比了两种籽晶氨热生长后晶体表面、生长速率、结晶质量、应力状况。光学显微镜表明两种籽晶生长后晶体的表面具有相似的丘状表面。氨热法生长速率较慢,化学机械抛光籽晶生长速率略高于粗磨籽晶。X射线单晶衍射(XRD)(002)和(102)的摇摆曲线半高宽显示抛光籽晶与粗磨籽晶生长得到GaN结晶质量基本一致。Raman E2(high)频移表明抛光籽晶生长的GaN晶体接近无应力状态,粗磨籽晶生长的晶体存在较小的压应力。

The surface damage of the seed crystal will lead to increased dislocations of the grown crystal. In order to reduce the damage to the surface of the seed crystal, a wafer processed by a multi-step process of rough grinding-finishing-polishing is generally used as the seed crystal. The complicated process involves many steps, and the cost is high. In this paper, the rough ground GaN with phosphoric acid to remove the surface damage layer and the chemical mechanical polished GaN were used as seed crystals respectively. The crystal surface, the growth rate, crystal quality and stress of the two seed crystals after ammonothermal growth were compared. The optical microscopy shows that the surface after the growth of the two seed crystals have similar hillocks. The growth rate of ammonothermal method is slow, and the growth rate of chemically mechanically polished seed crystal is slightly higher than that of rough ground seed crystal. The full width at half maximum(FWHM) of X-ray diffraction rocking curves of(002) and(102) planes show that the quality of GaN crystal obtained by the growth of polished seed crystal is basically the same as that of coarsely ground seed crystal. E2(high) frequency shift of Raman indicates that the GaN crystal grown on the polished seed crystal is close to the stress-free state, and the crystal grown on the coarsely ground seed crystal has a small compressive stress.