Temperature-dependent terahertz radiation from the surfaces of narrow-gap semiconductors illuminated by femtosecond laser pulses

摘要

Temperature-dependent increase of the terahertz (THz) electric field emitted from the surfaces of optically pumped narrow-gap semiconductors InAs, InSb, and CdxHg1-xTe is presented. In the case of Cd0.2Hg0.8Te increase up to 15-17 times has been observed, when cooling the sample from the room temperature to close to liquid-helium temperatures, and THz emission from this material becomes comparable to that of p-InAs emitter. This effect was explained in terms of the increased photoexcited electron excess energy due to the positive temperature coefficient for energy bandgap of CdxHg1-xTe, as well as by weaker surface field screening and carrier-carrier scattering. Temperature-dependent modification of the shape of THz pulses emitted from InSb surfaces has been observed and attributed to plasma oscillation of the cold electrons.