Abstract
Centimeter-sized Te-doped GaSe ingots were grown from the charge compositions of GaSe with nominals 0.05, 0.1, 0.5, 1, and 3 mass% Te, which were identified as ε-GaSe:Te (0.01, 0.07, 0.38, 0.67, and 2.07 mass%) single crystals. The evolution of the absorption peaks of the phonon modes E'(2) (≈ 0.584 THz) and E"(2) (1.77 THz) on Te-doping in GaSe:Te crystals was studied by THz time-domain spectroscopy. This study proposes that the evolution of both E'(2) and E''(2) absorption peaks correlates well with the optical quality of Te-doped GaSe crystals, which was confirmed by experimental results on the efficiency of THz generation by optical rectification. Maximal intensity of the absorption peak of the rigid layer mode E'(2) is proposed as a criterion for identification of optimal Te-doping in GaSe crystals.
Highlights
The optical properties of GaSe have been successfully used to generate coherent radiation in the mid-infrared and down to the terahertz (THz) frequency range [1, 2]
This paper reports the growth of centimeter-sized ingots with ε-GaSe:Te single crystals for non-linear applications
This study proposed that the evolution of E’(2) and E”(2) modes can be used to identify the lattice structure and the optical quality in Te-doped GaSe crystals, which was experimentally confirmed by the study of THz generation efficiency at various Te-doping levels
Summary
The optical properties of GaSe have been successfully used to generate coherent radiation in the mid-infrared and down to the terahertz (THz) frequency range [1, 2]. Because of the layer structure, GaSe crystals exhibit considerable anisotropic absorption at short-wavelength edges of visible and THz ranges, and at long-wavelength edge of mid-IR range. This study proposed that the evolution of E’(2) and E”(2) modes can be used to identify the lattice structure and the optical quality in Te-doped GaSe crystals, which was experimentally confirmed by the study of THz generation efficiency at various Te-doping levels. The THz generation efficiency from ∼0.3-mm-thick Te-doped samples with 0.07 mass% was over 20% higher than that in a pure GaSe crystal with same thickness, and was consistent with the highest absorption peak of the rigid layer mode E’(2). The doping-dependent evolution of the rigid layer mode E’(2) may be used as a criterion for identifying the optimal doping in GaSe or other crystals
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