Temperature dependence of transport properties of the two‐dimensional hole gas (2DHG) atp‐AlxGa1−xAs/GaAs heterostructures grown by molecular‐beam epitaxy (MBE) was investigated. A phenomenon in which the 2DHG vanishes at low temperatures is found in the samples that were grown in an insufficient outgassing condition and unintentionally highly doped with carbon. It is peculiar to the 2DHG system because of two reasons; one is that the effective mass of the holes is much larger than that of electrons, which results in the Fermi level of the system being more dependent on the acceptors in GaAs. The second is that the acceptor level in GaAs is deeper than the donor level in GaAs and holes are more easily trapped by the acceptor levels at low temperatures. To prevent the 2DHG disappearance, two methods were successfully applied; one is to reduce acceptors in unintentionally doped GaAs, and the other is to dope more Be acceptors in the AlxGa1−xAs layer. By outgassing the MBE apparatus sufficiently, a mobility of 83500 cm2/V s at 4.2 K has been achieved at hole concentrations ofps=2.0×1011cm−2in the 2DHG sample. The persistent photoconductivity (PPC) effect was also found in the sample whose 2DHG vanishes at 4.2 K. This fact shows that the carbon acceptor level works as a PPC center in GaAs.
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机译：研究了分子&连字符-束外延（MBE）生长的二维空穴气体（2DHG）atp‐AlxGa1−xAs/GaAs异质结构的温度依赖性.在脱气不足的条件下生长的样品中发现了2DHG在低温下消失的现象，并且无意中高度掺杂了碳。由于两个原因，它是 2DHG 系统所特有的;一是空穴的有效质量远大于电子的有效质量，这导致系统的费米能级更依赖于砷化镓中的受体。二是砷化镓中的受体能级比砷化镓中的供体能级更深，在低温下更容易被受体能级捕获空穴。为了防止2DHG消失，成功应用了两种方法;一种是减少无意掺杂的GaAs中的受体，另一种是在AlxGa1−xAs层中掺杂更多的Be受体。通过充分除气 MBE 装置，在 2DHG 样品中，在 ps=2.0×1011cm−2 的空穴浓度下，在 4.2 K 时实现了 83500 cm2/V s 的迁移率。在2DHG在4.2 K时消失的样品中也发现了持久光电导率（PPC）效应。这一事实表明，碳受体水平在砷化镓中起着PPC中心的作用。
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