ZnO LASER BY ELECTRON BEAM EXCITATION

Abstract

The wavelength of laser emission from an electron-beam-pumped ZnO was measured in the temperature range from 82 to 250°K. The laser emission occurred near the line due to the annihilation of a free exciton assisted by one LO phonon at 82°K. Above 180°K the laser emission occurred near the line due to the transition assisted by two LO phonons. From 130 to 170°K the laser oscillation appeared in two spectral lines. The temperature dependence of threshold current density measured from 82 to 250°K was weak compared with the theoretical curve based on the laser action involving the A-LO line.

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature: the self-absorption effect

“…Contrastingly and attractively, the TPA-PL exhibits a very dissimilar evolution trend in which the FX and DX principal lines (e.g. their ZPL lines) are almost fully eliminated for T >70 K, the FX-1LO peak then fully removed at T = 250 K, and the spectrum eventually completely dominated by the FX-2LO emission at 300 K. This temperature evolution tendency is well consistent with those reported by Iwai and Namba [13], as well as Klingshirn [15]. In fact, all reported room-temperature TPA-PL spectra of various ZnO always peak at $390 nm [7,15,[21][22][23][24].…”

“…In fact, all reported room-temperature TPA-PL spectra of various ZnO always peak at $390 nm [7,15,[21][22][23][24]. Even for all laser spectra of various forms of ZnO at room temperature, their spectral centers always located at $390 nm [1][2][3][4][5][6][8][9][10][11][12][13][14][15][16][17][22][23][24][25]. These highlyconsistent experimental data from different groups indicate that someone unified mechanism shall be responsible for the phenomenon.…”

“…For UV lasing emissions from ZnO single crystals, actually as early as in 1966, Nicoll [12] already reported the happening at 77 K by using electron beam as the pumping source. Several years later, Iwai and Namba [13] extended the study of electron-beam-pumped ZnO laser to a wider temperature range, i.e., 82-250 K. They found that the laser does not happen at so-called zero-phonon line (ZPL) of a free exciton. Instead of, it occurs near the line due to the annihilation of a free exciton assisted by one longitudinal optical (LO) phonon at 82 K. Above 180 K the laser emission redshifts toward the line due to the transition assisted by two LO phonons.…”

Passivation of active recombination centers in ZnO by hydrogen doping

“…The FX n peaks in the figures have been tentatively identified as nth phonon replicas of the free-exciton annihilation, according to prior studies. 29,30 The identification of the FX n peaks will be discussed later. For the CVT crystal, a strong FX 1 emission was observed above 100 K, both before and after irradiation, and the FX 2 peak was also obvious at the higher temperatures.…”

Phonon-assisted lasing in ZnO microwires at room temperature

“…Above 120 K, the main extent of bound excitons is dissociated and the thermal occupation of longitudinal optical (LO) phonon states leads to an enhanced absorption in the energy range between the free exciton energy and its first LO-phonon replica E FX -E FX-1LO . Hence, a transition from FX-1LO to FX-2LO lasing was observed at temperatures above 120 K. The respective FX-2LO recombination process was found to be stable up to 250 K in macroscopic single crystals [5][6][7]. At room temperature, the 2LO-phonon-assisted recombination of free excitons exhibits relatively low gain values with α ∼ 50 cm −1 [8] in contrast to the other possible gain processes such as exciton-exciton scattering with α ∼ 300 cm −1 [9] and electron-hole plasma (EHP) with α ∼ 10 3 − 10 4 cm −1 [10].…”