Terahertz gain on shallow donor transitions in silicon

Abstract

Small signal gain measurements of optically excited terahertz silicon lasers are reported. Two types of lasers, Si:P and Si:Bi, were investigated. They were optically excited with radiation from a free electron laser or a CO₂ laser. The experiments were performed with an oscillator-amplifier scheme where one sample serves as a laser while the other one is an amplifier. In case of the free electron laser the pump frequency corresponds to intracenter excitation of the 2p0 or 2p± states of the P and Bi Coulomb centers, and the gain was determined for the 2p0→1sE, 2p0→1sT2 transitions in Si:P and the 2p±→1sE transition in Si:Bi. Pumping with a CO₂ laser leads to photoexcitation of the Coulomb centers. In this case the gain was determined for the 2p0→1sT2 of Si:P transition. The gain for intracenter pumping is in the range 5−10 cm−1 while for photoexcitation the gain is considerably less, namely 0.5 cm−1. The experimental results are analyzed and found to be in good agreement with theoretical calculations based on balance equations. © 2007 American Institute of Physics. DOI: 10.1063/1.2804756