Recombination processes in unintentionally doped GaTe single crystals

Abstract

Emission spectra of GaTe single crystals in the range of 1.90-1.38 eV have been analyzed at different temperatures and excitation intensities by photoluminescence, photoluminescence excitation, and selective photoluminescence. A decrease in band gap energy with an increase in temperature was obtained from the redshift of the free exciton recombination peak. The energy of longitudinal optical phonons was found to be 14Ϯ1 meV. A value of 1.796Ϯ0.001 eV for the band gap at 10 K was determined, and the bound exciton energy was found to be 18Ϯ0.3 meV. The activation energy of the thermal quenching of the main recombination peaks and of the ones relating to the ionization energy of impurities and defects was analyzed. The results obtained show the existence of two acceptor levels with ionization energies of 110Ϯ5 and 150Ϯ5 meV, respectively, and one donor level with an ionization energy of 75Ϯ5 meV. The study of chemical composition by inductively coupled plasma-optical emission spectroscopy and x-ray energy dispersion spectroscopy shows the existence of Na, Li, and Si. Sodium and lithium impurities could be associated with acceptor levels at gallium substitutional sites, and silicon ones with a donor level at Ga sites, whose vacancies can also be involved in these electronic levels.

Lattice Vibration of Layered GaTe Single Crystals

“…Ten energy peaks are observed. Among them, the eight located at 109.6 cm −1 , 114.5 cm −1 , 151.7 cm −1 , 161.6 cm −1 , 175.2 cm −1 , 209.6 cm −1 , 267.1 cm −1 , 281.7 cm −1 match previous reports for monoclinic GaTe single crystals [18][19][20]24]. However, there is still controversy over the interpretation of the other two situated at 129.4 cm −1 and 141.8 cm −1 .…”

“…Band C has a strong and sharp peak centered at 1.7785 eV, with the full-width at half maximum (FWHM) of only 3 meV, which is sharper than the reported GaTe band [23,24]. According to the established band gap levels and recombination process in GaTe single crystals [23,24], the band A belongs to donor-acceptor pair (DAP) transitions from a donor level situated at around 80 meV below the conduction band to an acceptor level 150 meV over the valence band. The band B consists of two peaks located at 1.72 eV and 1.76 eV, respectively, formed by the recombination of excitons trapped in two acceptor levels with ionization energies of 110 meV and 150 meV.…”

Thermal Creation of Defects in GaTe

“…The FB involving the conduction band and A 1 acceptor and the DAP involving the donor (D) and the A 2 acceptor were already described in a previous study. 18) The new DAP 0 involving shallow defects is shown. The deep defect responsible of the peak 0.76 eV is located with the corresponding recombination process involving a shallow donor with an ionization energy of around 40 meV.…”

“…The band centered at 1.57 eV corresponds to a donor-acceptor pair (DAP) recombination. The existence of at least one donor and two acceptor levels with ionization energies ranging from 75 to 150 meV was deduced from selective excitation PL, excitation PL and temperature dependent PL 18) measurements. Figure 1 also shows the spectra of samples annealed at 200 and 400 C. Their intensity was normalized to the total intensity integrated from 1.5 to 1.8 eV.…”

Temperature- and illumination-induced charge-state change in divacancies of GaTe

“…Other authors studied the recombination of free excitons [8][9][10][11][12] by photoluminescence ͑PL͒. The free to bound and donor-acceptor pair PL recombinations in the near-band edge [13][14][15][16] and time resolved PL at 4 K ͑Ref. 17͒ have been also studied.…”