NH3流量调控Ⅴ/Ⅲ比对HVPE生长GaN薄膜的影响

氢化物气相外延(HVPE)法具有生长成本低、生长条件温和、生长速率快等优点,被认为是生长高质量GaN单晶衬底的最有潜力的方法。为了优化HVPE生长GaN的条件,通过改变NH3流量调控Ⅴ/Ⅲ比(NH3流量与HCl流量之比)。通过建立简单的生长模型,对不同Ⅴ/Ⅲ比下GaN薄膜形态变化的机理进行了分析,研究了HVPE生长过程中氮源(Ⅴ族)和镓源(Ⅲ族)不同流量比对结晶质量和表面形貌的影响。实验结果表明,低Ⅴ/Ⅲ比会导致成核密度低,岛状晶胞难以合并;高Ⅴ/Ⅲ比会降低表面Ga原子的迁移率,导致表面高度差异大,结晶质量差。与Ⅴ/Ⅲ比为15.000和28.125相比,Ⅴ/Ⅲ比为21.250时更适合GaN薄膜生长,得到的晶体质量最高。

Influence of Ⅴ/Ⅲ Ratio by Controlling NH3 Flow Rate on HVPE Growth of GaN Thin Film

Hydride vapor phase epitaxy(HVPE)method is the most promising approach to grow high quality GaN single crystal substrate for its low cost,mild growth condition and fast growth rate,etc.Ⅴ/Ⅲratio(the ratio of NH3 flow rate and HCL flow rate)was controlled by changing the NH3 flow rate in order to optimize the conditions for growing GaN by HVPE.The mechanism of morphological changes under differentⅤ/Ⅲratios was analyzed by establishing a simple growth model.The influences of different flow ratios of nitrogen source(groupⅤ)and gallium source(groupⅢ)on crystal quality and surface morphology of GaN thin films prepared by HVPE were studied.Test results show that lowⅤ/Ⅲratio leads to low nucleation density,and island cells are hard to merge;highⅤ/Ⅲratio reduces the mobility of surface Ga atom,resulting in large difference in surface height and poor crystal quality.TheⅤ/Ⅲratio of 21.250 is the most suitable condition for GaN thin film growth,and the crystal quality is the highest compared with those at theⅤ/Ⅲratios of 15.000 and 28.125.