基于变温霍尔效应方法的一类n-GaN位错密度的测量

Determination of dislocation density of a class of n-GaN based on the variable temperature Hall-effect method

结合莫特相变及类氢模型,采用浅施主能量弛豫方法,计算了一类常见n-Ga N光电子材料的载流子迁移率,给出了精确测定其刃、螺位错密度的电学方法.研究表明,对于莫特相变材料(载流子浓度超过1018cm^(-3)),以位错密度Ndis、刃螺位错密度比β、刃位错周围浅施主电离能εD1、螺位错周围浅施主电离能εD2为拟合参数的载流子迁移率模型与实验曲线高度符合,拟合所得刃、螺位错密度与X射线衍射法或化学腐蚀方法的测试结果也基本一致.实验结果表明,莫特相变材料虽然载流子浓度高、霍尔迁移率低,但其位错密度却并不一定高过载流子浓度低、霍尔迁移率高的材料,应变也无明显差异,因此,莫特相变与刃、螺位错密度及两类位置最浅的施主均无关系,可能是位置较深的施主或其他缺陷所致,需要比一般杂质带高得多的载流子浓度.该方法适合霍尔迁移率在0 K附近不为零,霍尔迁移率曲线峰位300 K左右及以上的各种生长工艺、各种厚度、各种质量层次的薄膜材料,能够对迁移率曲线高度拟合,迅速给出莫特相变材料的相关精确参数.

An analytical model for electron mobility in a class of wurtzite n-Ga N,whose carrier concentration is over 1018cm^-3（Mott＇s critical limit）,is developed.With the dislocation density and two donor levels serving as the important parameters,the proposed model can accurately predict the electron mobility as a function of temperature.The edge and screw dislocation densities in two samples,which are respectively grown on sapphire（001） by metal organic chemical vapor deposition and hydride vapor phase epitaxy,are determined by using this model which is discussed in detail.It is shown that the data-fitting of μH-T characteristic curve is a highly suitable technique for accurately determining the edge and screw dislocation densities in n-Ga N films.Quantitative analyses of donor concentration and donor activation energy indicate that the impurity band occurs when the carrier concentration is under 1017cm^-3,much lower than the critical carrier concentration of Mott transition（1018cm^-3）.Such a behavior can also be confirmed by the results from solving the Boltzmann transport equation by using the Rode iterative method.Another anomaly is that the dislocation density in Mott transition material perhaps is lower than that of material with carrier concentration under 1018cm^-3.This fact indicates that the cause of Mott transition should not be the shallow donor impurities around dislocation lines,but perhaps the deeper donor impurities or other defects.In the theoretical model calculation,two transition characteristics together with the donor distribution and its energy equilibrium are taken into account.Based both on the Mott transition and the H-like electron state model,the relaxation energies for the shallow-donor defects along the screw and edge dislocation lines are calculated by using an electrical ensemble average method.Besides,an assumption that should be made is that there are 6 shallow-donor defect lines around one dislocation line.The research results show that the Hall mobility should be taken as the live degree of the ionizing energy for the shallow-donor defects along the dislocation line.The experimental results indicate that our calculation function can be best fit by the experimental curve,with the values of dislocation density being between our model and others determined by X-ray diffraction or by chemical etching method,which are all in good agreement with each other.The method reported can be applied to the wurtzite n-Ga N films grown by various preparation technologies under any condition,with the peak-mobility temperature about or over300 K,whose Hall mobility near 0K perhaps is over 10 cm^2/（V·s） and even 100 cm^2/（V·s）.