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Si：P中的THz激光振荡现象，并讨论了Si：P中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Si：P样品，其六个平行表面经过精确抛光。将其置于液态He中，用1MWTEA CO_2激光激发。Ge：As探测器探测到了THz辐射.我们确认了激光，因为发射强度对激发光的入射角敏感，并且发射在激发强度依赖性方面具有阈值。为了研究探测器的特性，测量了Ge：As和Ge：Zn在TEA CO_2激光激发下的红外光电导。Ge：As和Ge：Zn分别呈超线性和亚线性关系。我们测量了Ge的红外光电导，详细研究了Ge的杂质能级。在Ge：As和Ge：Zn中，除了声子吸收外，在120和115 meV附近还观察到光电导的降低。这两个m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，观察到类似Fano共振的结构，估算出ls（T_2）激发态的电离能为10.5meV。Ge中的深杂质所利用的THz激光器可以在5meV附近振荡，这比Si：P激光器低得多，因为尽管有深杂质，ls（T2）态还是相当浅的。

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.