Research on THz laser utilizing deep impurities in semiconductors

通过对Ge：As、Ge：Zn和Ge：Te中杂质能级的红外光电导研究，证实了THz激光在Si：P中的振荡，并讨论了THz激光振荡的可能性。德国DLR研究所提供了一个5×7×7 mm^3矩形的Si：P样品，六个平行的表面被精确抛光。用1 mW的TEA CO_2激光激发。用Ge：As探测器探测到太赫兹辐射。我们确认了激光，因为发射强度对激发光的入射角很敏感，而且发射在激发强度依赖时有一个阈值。为了研究探测器的特性，用TEA CO_2激光器测量了Ge：As和Ge：Zn的红外光电导。Ge：As和Ge：Zn分别存在超线性和亚线性关系。为了详细研究Ge中的杂质能级，我们测量了红外光电导。除声子吸收外，Ge：As和Ge：Zn分别在120 meV和115 meV附近观察到光电导的降低。这两个m都对应于自由电子通过发射LO声子而跃迁到杂质的激发态。在Ge：Te中，观察到了类似Fano共振的结构，估算出ls(T2)激发态的电离能为10.5 meV。Ge中的深杂质利用的THz激光可以在5 meV左右振荡，远低于Si：P激光器，这是因为尽管有深杂质，ls(T2)态却相当浅。

We have confirmed THz laser oscillation in Si : P and discussed possibility of THz laser oscillation by investigating impurity level by infrared photoconductivity in Ge : As, Ge : Zn and Ge : Te. DLR Institute in Germany supplied a Si : P sample of 5×7×7mm^3 rectangular shape with six parallel surfaces polished exactly. It was placed in liquid He and excited by 1MW TEA CO_2 laser. THz emission was detected a Ge : As detector. We confirmed lasing because emission intensity is sensitive to the incident angle of excitation light and the emission has a threshold in excitation intensity dependence. In order to characteristic of the detector infrared photoconductivity was measured in Ge : As and Ge : Zn eicited by TEA CO_2 laser. Super and sub linear dependences were observed fofr Ge : As and Ge : Zn, respectivevly. We measured infared photoconductivity to study impuritylevel in Ge in detail. In addition to phonon absorption, decrease of phohtoconductivity was observed around 120 and 115 meV in Ge : As and Ge : Zn, respectively. Both of the m correspond to transition of a free electron to the excited state of impurity by emitting LO phonon. In Ge : Te, structures like Fano resonances were observed and the ionization energy of ls(T2) excited state was estimated to be 10.5meV. The THz laser utilized by deep impurities in Ge may oscillate around 5meV much lower than Si : P laser because the ls(T2) state is considerably shallow in spite of a deep impurity.