Free-carrier and phonon properties of n- and p-type hexagonal GaN films measured by infrared ellipsometry
Free-carrier and phonon properties of n- and p-type hexagonal GaN films measured by infrared ellipsometry
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DOI：
10.1103/physrevb.62.7365
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发表时间：
2000-09-15
影响因子：
3.7
通讯作者：
Tiwald, TE
中科院分区：
文献类型：
--
作者：
Kasic, A;Schubert, M;Tiwald, TE
利用红外椭圆偏振光谱仪（IRSE）在300 ~ 1200 cm（-1）的波数范围内测量了高阻、Si掺杂的n型和Mg掺杂的p型α-GaN的各向异性室温光学性质。大约1 μ m厚的薄膜沉积在c-平面蓝宝石上的分子束外延没有缓冲层。自由载流子浓度从霍尔测量获得。IRSE数据进行了分析，通过模型计算的红外光学介电函数平行（平行）和垂直（垂直）的α-GaN薄膜的c轴。我们得到了薄膜声子频率和加宽值和光学迁移率和有效质量参数的n型和p型的α-GaN。与Perlin等人[Appl.Phys.Lett. 68，1114（1996）]我们确定有效电子质量为m（e.垂直于）/m（0）= 0.237+/-0.006和m（e.平行于）= 0.228 +/-0.008。对于空穴浓度N-h = 8 × 10（17）cm（-3）的p型GaN，我们发现m（h）/m（0）= 1.40 +/- 0.33，这与纤锌矿GaN中Rashba-Sheka-Pikus参数的最新理论研究一致。然而，没有获得在25%以内的有效孔质量的实质各向异性。椭圆偏振数据还允许导出几乎各向同性的模型量ε（无穷大，j）（j=垂直于，平行于），但可以根据膜是未掺杂的还是掺杂的而在4.92和5.37之间变化。在重Si掺杂的n型α-GaN中，我们观察到薄的载流子耗尽表面层和在574、746和851 cm（-1）处的额外红外活性振动模式。还进行了GaN薄膜的拉曼测量，并将测量结果与IRSE研究结果进行了比较。
Infrared spectroscopic ellipsometry (IRSE) over the wave-number range from 300 to 1200 cm(-1) is used to determine the anisotropic room-temperature optical properties of highly resistive, Si-doped n-type and Mg-doped p-type alpha-GaN. The approximately 1-mu m-thick films were deposited on c-plane sapphire by molecular beam epitaxy without a buffer layer. The free-carrier concentrations are obtained from Hall measurements. The IRSE data are analyzed through model calculations of the infrared optical dielectric functions parallel (parallel to) and perpendicular (perpendicular to) to the c axis of the alpha-GaN films. We obtain the thin-film phonon frequencies and broadening values and the optical mobility and effective-mass parameters for n- and p-type -alpha-GaN. In agreement with Perlin et al. [Appl. Phys. Lett. 68, 1114 (1996)] we determine the effective electron masses as m(e.perpendicular to)/m(0) = 0.237+/-0.006 and m(e.parallel to) = 0.228 +/- 0.008. For p-type GaN with hole concentration N-h = 8 x 10(17) cm(-3) we find m(h)/m(0) = 1.40 +/- 0.33, which agrees with recent theoretical studies of the Rashba-Sheka-Pikus parameters in wurtzite GaN. However, no substantial anisotropy of the effective hole mass is obtained to within 25%. The ellipsometry data also allow for derivation of the model quantities epsilon(infinity,j) (j=perpendicular to,parallel to) which are almost isotropic but may vary between 4.92 and 5.37 depending on whether the films are undoped or doped. In heavily-Si-doped n-type alpha-GaN we observe a thin carrier-depleted surface layer and additional infrared-active vibrational modes at 574, 746, and 851 cm(-1). Raman measurements of the GaN films are also performed, and the results are compared to those obtained from the IRSE investigations.