Dresden 2017 – scientific programme

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DS: Fachverband Dünne Schichten

DS 32: Focussed Session: Oxide Semiconductors for Novel Devices II

DS 32.2: Talk

Wednesday, March 22, 2017, 15:15–15:30, CHE 89

Photo- and electroluminescence of chromium doped β-Ga₂O₃ — •Andreas Fiedler, Zbigniew Galazka, and Klaus Irmscher — Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin, Germany

Chromium doped β-Ga₂O₃ single crystals were grown by the Czochralski method. The Cr doping produces a greenish coloration of the crystal, which results from two broad absorption bands centered at wavelengths of about 450 nm and 600 nm, respectively. Similar absorption bands are well know from Al₂O₃:Cr (ruby) and assigned to Cr³⁺ on Al site. This suggest that in the β-Ga₂O₃:Cr crystals Cr prefers Ga site occupation in the Cr³⁺ oxidation state. In analogy to ruby, we also see the characteristic red photoluminescence (PL) line due to an intra-center transition of Cr³⁺. The PL line of ruby at 694.3 nm is shifted to 695.6 nm in β-Ga₂O₃:Cr due to the different ligand field. The PL was characterized between 4.2 K and 300 K. With increasing temperature an increasing broadening of the PL peak occurs. The excited state has a lifetime of 160 µs at room temperature, which makes it possible to generate a population inversion. In contrast to ruby, our β-Ga₂O₃ is semiconducting, hence an electroluminescence can be generated by electron impact excitation, which shows two transitions at 695.1 nm and at 696.2 nm. The beat frequency of these transitions is 0.7 THz, which is in the so called terahertz gap. This may be used for a terahertz laser, which opens a new field of applications for β-Ga₂O₃ beside the power devices and the photo detectors.