变温吸收谱研究液相外延碲镉汞浅能级

利用变温吸收谱(11—300K)对非故意掺杂液相外延Hg_1-xCd_xTe进行研究,对吸收边在低温区间(<70K)出现的约7—20meV反常移动现象进行了分析.结果表明该现象是由材料中Hg空位作为受主能级存在而形成的,红移幅度与样品组分/载流子浓度有关.据此估算Hg空位大致位于价带上方约20meV,与Hg空位形成浅受主能级的经验公式计算结果基本符合.该结果可以解释由传统吸收谱方法确定材料禁带宽度略高于材料实际光电响应截止能量值的现象. 关键词： 碲镉汞 液相外延 汞空位 反常吸收

Temperature-dependent absorption spectra investigation of shallow levels in HgCdTe grown by liquid phase epitaxy

Temperature-dependent absorption spectra in temperature range of 11—300K are recorded for a series of unintentionally doped HgCdTe grown by liquid phase epitaxy. The abnormal energy shift of about 7—20meV of absorption edge in the low temperature range (<70K) has been analyzed. The results suggest this the phenomenon to be caused by the Hg vacancies and the abnormal red-shift is related to the composition and the carrier density of the materials. The Hg vacancy level is estimated to be at 20meV above the valence band, which is well consistent with the results of Hg vacancy acceptor level calculated by the empirical expression. The results may provide a preliminary explanation that the bandgap obtained by the conventional transmission spectroscopy is slightly higher than the cutoff energy of the photocurrent response in practical device applications.