Direct versus indirect optical recombination in Ge films grown on Si substrates
Direct versus indirect optical recombination in Ge films grown on Si substrates
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DOI：
10.1103/physrevb.84.205307
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发表时间：
2011-11-11
影响因子：
3.7
通讯作者：
Menendez, J.
中科院分区：
文献类型：
--
作者：
Grzybowski, G.;Roucka, R.;Menendez, J.
Si上Ge薄膜的光发射光谱与体Ge薄膜的光发射光谱有明显的不同。而体锗发射主要是由材料的间接带隙，从锗薄膜的光致发光信号主要是与它的直接带隙。使用一类新的Ge-Si薄膜生长最近推出的化学气相沉积方法，我们研究了直接和间接的光致发光的本征和掺杂样品，我们得出结论，这种差异的起源是缺乏自吸收的Ge薄膜结合从准平衡条件的偏差，在导带的未掺杂的薄膜。后者证实了一个简单的模型表明，从准平衡的偏差是由短得多的复合寿命的薄膜相对于体锗。
The optical emission spectra from Ge films on Si are markedly different from their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the material's indirect gap, the photoluminescence signal from Ge films is mainly associated with its direct band gap. Using a new class of Ge-on-Si films grown by a recently introduced chemical vapor deposition approach, we study the direct and indirect photoluminescence from intrinsic and doped samples and we conclude that the origin of the discrepancy is the lack of self-absorption in thin Ge films combined with a deviation from quasi-equilibrium conditions in the conduction band of undoped films. The latter is confirmed by a simple model suggesting that the deviation from quasi-equilibrium is caused by the much shorter recombination lifetime in the films relative to bulk Ge.