Carrier dynamics and lasing in epitaxial ZnTe layers on GaAs

Abstract

By means of ps-time resolved luminescence measurements the carrier dynamics in ZnTe/GaAs epitaxial layers of different thicknesses are investigated. A linear decay process corresponding to exciton recombination at low and a quadratic process corresponding to the recombination in an electron-hole plasma (EHP) at high excitation, respectively, are observed. The decay processes are dominated by the carrier diffusion into the substrate. The lifetime, binding energy, and temperature of the plasma are extracted from the time-resolved luminescence spectra. The carrier density found from the luminescence fit is used to describe the band-gap renormalization effect in ZnTe/GaAs epilayers at high excitation. Laser emission from all samples is observed at low and even up to room temperatures.

Observation of superfluorescence from a quantum ensemble of coherent excitons in a ZnTe crystal: Evidence for spontaneous Bose-Einstein condensation of excitons

“…1(d) shows ordinary build-up followed by accelerated exciton recombination on P. This is typical of an electronhole plasma (EHP) [15]. Whereas exciting other areas of the sample, we observe the onset of "lasing" for the I1 line as P>P 0 , as observed before [27], now the I1 peak has greatly increased intensity and undergoes a large red-shift to 524.5 nm (2.364 eV) at P=18 mW and its linewidth narrows to 3.2 nm (14 meV) ( Fig. 1(b)).…”

“…These include: ruby:Cr 3+ [18], GaAs laser diodes [19], ZnO nano-materials [20,21], CuCl quantum dots [22], diphenyl:pyrene [23], Rphycoerythrin [24], thiophene/phenylene co-oligomer [25]. ZnTe crystals, as the model II-VI direct-gap intrinsic semiconductor, have been used to attempt to observe BEC of excitons [26], and efforts have been made to resolve the lasing behaviour from highly excited ZnTe epitaxial layers with a τ p =70 ps [27]. Here we report exciton dynamics with femtosecond resolution in ZnTe crystals at 5 K studied by the femtosecond time-resolved fluorescence technique [28], showing clear observation of SF emission.…”

Superradiant Lasing and Collective Dynamics of Active Centers with Polarization Lifetime Exceeding Photon Lifetime

“…(Here the term "superfluorescence" is used instead of the more common term "SR" because in many experimental and theoretical works the latter implies that there is some preliminary coherent resonant pulse initiating a collective spontaneous emission.) Similar observations are made for the superfluorescent recombination in semiconductor samples with modest inhomogeneous broadening of active particles, which include free electrons and holes in magnetized GaAs quantum wells [21,22], degenerate electronhole gas in semiconductors [29], excitons in ZnTe crystals [10,34], and In-centers in Cd 0.8 Zn 0.2 T e crystals [13]. Based on CW pumping, the class D lasers are expected [31] to have variety of operation regimes, rich multi-mode spectra, and flexible pulse profiles, which are promising for the pulse shaping technologies and the pulse processing in "information optics" [18,39,45].…”