Berlin 2018 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 10: Nitrides: Devices
HL 10.3: Talk
Monday, March 12, 2018, 15:30–15:45, EW 203
AlxGa1−xN:Mg short period superlattice cladding layers with x ≥ 0.6 for UVC laser diodes — •C. Kuhn1, M. Guttmann1, N. Susilo1, M. Martens1, F. Mehnke1, L. Sulmoni1, T. Wernicke1, and M. Kneissl1,2 — 1Technische Universität Berlin, Institute of Solid State Physics, Berlin, Germany — 2Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin, Germany
Key challenges for the realization of UVC laser diodes with emission wavelength below 270 nm are carrier injection, light absorption and waveguiding. The waveguiding requires low loss AlxGa1−xN cladding layers with high aluminum content x > 0.7. However, this limits efficient carrier injection due to the typically high resistance of Mg-doped AlGaN layers. To increase the conductivity short period superlattices (SPSL) can be implemented. Nevertheless, a high conductivity and its accurate determination still remains particularly demanding, especially for high Al contents.
This paper investigates the optical and electrical properties of AlGaN:Mg SPSLs up to x = 0.8. Such high Al contents shift the absorption edge far away from the lasing wavelength resulting in low absorption < 50 cm−1 in the layers due to Mg-related transitions. AlGaN:Mg SPSLs with average x = 0.22 exhibit a relatively low lateral resistivity of 0.6 Ωcm which strongly increases to 70 Ωcm for transparent AlGaN:Mg with x = 0.6. Vertical resistivity measurements hint to an additional field-induced ionization of the Mg acceptors leading to an increase of the turn-on voltage, but allowing for relatively low series resistances and high pulsed current densities up to 5 kA/cm2.