Effect of uniaxial stress on intervalley phonon-assisted relaxation of excited shallow-donor states in silicon

Results of calculations of the rate of intervalley scattering for excited states 2p _±, 2p ₀, and 1s of the Group V donors (phosphorus, antimony, and arsenic) in silicon in the case of electron-phonon interaction are reported. Anisotropy of the effective mass and degeneracy of electron states (related to six valleys for the conduction band) are taken into account. The extent of the effect of the shift of the energy of the ground state due to the potential of the central cell on the process of relaxation for various donors has been determined. The main attention has been paid to the dependence of the relaxation rate on the compressive strain of silicon in the crystallographic direction [100]. It is established that such strain can appreciably increase the lifetimes of working states in a laser operating on intracenter transitions for donors in silicon and increase the quantum efficiency and gain of such active medium.     

Terahertz absorption and emission upon the photoionization of acceptors in uniaxially stressed silicon

Experimental data on the spontaneous emission and absorption modulation in boron-doped silicon under CO₂ laser excitation depending on the uniaxial stress applied along the [001] and [011] crystallographic directions are presented. Room-temperature radiation is used as the probe radiation. Low stress (less than 0.5 kbar) is shown to reduce losses in the terahertz region by 20%. The main contribution to absorption modulation at zero and low stress is made by A⁺ centers. Intersubband free hole transitions additionally contribute to terahertz absorption at higher stress. These contributions can be minimized by compensation.     

Shallow-donor lasers in uniaxially stressed silicon

The effects of the terahertz-stimulated emission of Group-V donors (phosphorus, antimony, arsenic, bismuth) in uniaxially stressed silicon, excited by CO₂ laser radiation are experimentally studied. It is shown that uniaxial compressive stress of the crystal along the [100] direction increases the gain and efficiency of stimulated radiation, significantly decreasing the threshold pump intensity. The donor frequencies are measured and active transitions are identified in stressed silicon. The dependence of the residual population of active donor states on the uniaxial compressive stress along the [100] direction is theoretically estimated.     

On the phonon-assisted relaxation of excited bismuth donor states in uniaxially stressed silicon

The low-temperature phonon-assisted relaxation rates of the excited states of bismuth donors in a silicon crystal uniaxially stressed in the [100] crystallographic direction are calculated. The states belonging to the lower (2Δ) and upper (4Δ) valleys of the silicon conduction band are considered. It is shown that the population inversion of bismuth donor states in the upper (4Δ) valleys of the silicon conduction band under optical pumping is possible.     

Relaxation of excited donor states in silicon with emission of intervalley phonons

The process of low-temperature relaxation of excited states of Group V donors in silicon due to coupling of electrons bound at Coulomb centers with intervalley phonons is analyzed. The rate of transitions from the 2p ₀ state to the group of 1s(E, T ₂) states with emission of the intervalley acoustic phonons LA-g and TA-f is calculated for the phosphorus, antimony, arsenic, and bismuth donors. It is shown that the TA-f phonons make a substantial contribution to nonradiative decay of the 2p ₀ state that controls the stimulated infrared emission of the phosphorus and antimony donors in silicon.