V. P. Sinis

Resonant acceptor states and terahertz stimulated emission of uniaxially strained germanium

The stimulated emission spectrum of uniaxially strained p-Ge is presented. The energy spectrum of the states of a shallow acceptor in Ge under uniaxial compression is calculated. The threshold pressure at which the acceptor state split off from the ground state becomes resonant is found. The pressure dependence of the width of this resonant level is calculated. The stimulated emission lines are identified. In particular, it is shown that the principal emission peak corresponds to the transition of holes from the resonant 1s (1sr) state to the local p±1 state. The probabilities of optical transitions are calculated. A mechanism of population inversion due to the intense resonant scattering of hot holes with an energy corresponding to the position of the 1sr level is proposed.

Gunn domains and stimulated far-infrared radiation in p-Ge under uniaxial deformation

Abstract The influence of electrical domain formation on far-infrared radiation in p-Ge at uniaxial compression was studied. The intensity of the spontaneous radiation was shown to be controlled by the domain length. The reciprocal influence of domain instability and stimulated far-IR emission was observed.

Hot carrier effect on resonant state THz laser operation

A comprehensive theoretical study of the operation of the strained hot hole p-Ge RSL is performed. Hot hole kinetics in strained p-Ge under an applied electric field is studied and heavy and light hole distribution functions are found as a solution to the Boltzmann kinetic equation, which includes interactions with acoustic and optical phonons, as well as resonant and nonresonant ionized impurity scattering. Nonequilibrium population of the localized acceptor states is obtained as a solution to the system of rate equations within the two-level model for an impurity level structure. Conditions for the formation of the intracentre population inversion are studied as a function of the electric field and external strain. We have observed that the population inversion is formed in a wide range of electric fields and, therefore, could be easily achieved. Net gain at the THz frequencies is calculated using the nonequilibrium hot hole distribution function and the localized states population. The possibility of achieving net THz gain in semiconductors by injection of hot carriers into impurity resonant states is demonstrated.

Stimulated THz emission of acceptor-doped SiGe/Si

An intense THz emission was observed from strained SiGe/Si quantum-well structures under strong pulsed electric field. The p-type structures were MBE-grown on n-type Si substrate and δ-doped with boron. Lines with wavelengths near 100 microns were observed in the emission spectrum. The modal structure in the spectrum gave evidence for the stimulated nature of the emission. The origin of the THz emission was attributed to intracenter optical transitions between resonant and localized boron levels.

Far-infrared lasing due to intracenter optical transitions in Ge

Stimulated emission of far-IR radiation from uniaxially compressed p-Ge in strong electric fields is shown to be due to population inversion of strain split acceptor levels. The peak corresponding to the optical transitions between split- off and ground acceptor states is found in the spectrum of stimulated emission. The strong frequency tuning by stress due to pressure dependence of the energy splitting of these states is obtained. The inversion takes place as the split- off acceptor state is in the valence band continuum.

Hot-Hole Streaming in Uniaxially Compressed Germanium

The streaming motion of charge carriers occurs in sufficiently strong electric field provided that the threshold scattering mechanism (e.g. optical-phonon emission) exists. It is the cyclic process consisted of scattering-free acceleration of holes up to the optical-phonon energy, emission of an optical phonon and the return to the region of small energies (so called “a source”) after which the process repeats. In this case, the distribution function in momentum space is stretched out along the field direction. The uniaxial stress removes the degeneracy of the valence band of Ge at k = 0 and splits it into two subbands separated by the energy gap Δ proportional to the stress P. In this work we studied spontaneous far-infrared radiation from stressed p-Ge. It will be shown that the limiting energy for ballistic acceleration of holes in the higher-energy subband is the energy corresponding to the hole transition to the lower-energy band via optical-phonon emission and the dynamics of hole heating in stressed p-Ge is strongly influenced by inter-subband optical-phonon scattering

Induced Radiative Transitions between Strain-Split Acceptor Levels in Germanium at Strong Electric Field

Earlier we have observed the induced far-infrared emission from uniaxially compressed p-Ge at strong electric field but with no magnetic field [1]. The possible reason for the induced emission was shown to be a population inversion of strain-split shallow acceptor levels [2]. In this report we present the first spectral investigations of the induced radiation carried out by means of far-infrared grating monochromator. The data obtained show that the induced emission in compressed p-Ge is due to the radiative transitions between strain-split impurity levels when the one of them lies in a continuous band spectrum.