Liquid-phase epitaxy of GaSe and potential application for wide frequency-tunable coherent terahertz-wave generation

• Published in: Journal of crystal growth Vol. 310; no. 7; pp. 1923 - 1928
• Main Authors: Oyama, Yutaka, Tanabe, Tadao, Sato, Fumikazu, Kenmochi, Atsushi, Nishizawa, Jun-ichi, Sasaki, Tetsuo, Suto, Ken
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.04.2008; Elsevier
• Subjects: A1. Point defects; A2. Growth from solutions; B1. Gallium compounds; B2. Nonlinear optic materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Iii-v semiconductors; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Nonlinear optical crystals; Optical materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optics; Physics; 74.25.Gz; 78.20.−e; A1. Point defects; B2. Nonlinear optic materials; 73.61.Le; 61.50.Nw; 78.20.Ci; A2. Growth from solutions; B1. Gallium compounds; LPE; Stoichiometry; Frequency dependence; Transparency; Non linear material; Molecular structure; Absorption coefficients; Intermolecular interaction; Organic molecule; Resonance frequency; Optical properties; Absorption spectra; Defect structure; Selenium; Gallium compounds; Nonlinear optics; Growth from solution; Wave absorption; Aluminium arsenides; Point defects; Vacancies; Semiconductor materials; Al. Point defects; A2. Growth from solutions; Bl. Gallium compounds; B2. Nonlinear optic materials; Growth mechanism; Optical materials; Resonance; Gallium selenides; 61.50.Nw; 73.61.Le; 74.25.Gz; 78.20.-e; 78.20.Ci
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2007.11.205

GaSe is one of the most promising semiconductor crystals for wide frequency-tunable terahertz (THz) wave generation by photo mixing. The ε-type monocrystalline GaSe crystals were successfully grown by the liquid-phase epitaxy at constant and low (530–590 °C) growth temperatures under the controlled different selenium (Se) vapor pressures ( P Se∼0–7.75 Torr). From the coherent THz-wave spectroscopy, the absorption spectra have shown different resonant frequencies and absorption coefficients due to the stoichiometry-dependent point defects which depend on the applied P Se. It is shown that the resonance in GaSe under P Se∼0 Torr shifts towards the lower THz frequencies compared with those under high P Se, maybe due to the degraded intermolecular interactions caused by the introduction of Se vacancy-related defects. The absorption coefficients (1–5 THz) decreased according to the increase of Se vapor pressure, thus the transparency of GaSe under higher P Se is improved by an amount of 25% compared with that of Bridgman-grown crystals. By using Bridgman-grown GaSe crystals, coherent-THz wave was generated by the difference frequency method (DFM) in a wide frequency range of 0.1–70 THz. Coherent-THz spectroscopy is a revolutionary method for the evaluation of molecular structures and defects in organic molecule also could be analyzed.