Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 72: Nitrides: Devices
HL 72.2: Talk
Thursday, March 23, 2017, 09:45–10:00, POT 06
Optoelectronic Characterization of AlGaN-based MSM-UV-Photodetectors — •Sebastian Walde, Moritz Brendel, Sylvia Hagedorn, Frank Brunner, Ute Zeimer, and Markus Weyers — Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
The alloy AlxGa1−xN used as absorber material in photodetectors (PD) offers a high sensitivity in the UV with cut-off wavelength between 200 nm (AlN) and 365 nm (GaN), adjustable by the Al-content x. A metal-semiconductor-metal (MSM) design has the advantage of a relatively simple layout, which makes it easy to fabricate and suitable for analyzing material properties of the underlying epitaxial layers.
We present results of bottom-illuminated MSM-UV-PD with Al0.5Ga0.5N absorber layers of different thicknesses tabs. The structures grown on AlN/sapphire exhibit a saturation of the external quantum efficiency (EQE) above specific saturation voltages. Two different carrier collection mechanisms can be observed and they are distinguished by different saturation regimes. The first is dependent on tabs and can be explained by the extension of the space charge region below the biased electrode. In that case, EQE at a wavelength of 250 nm saturates above 40 V for tabs = 500 nm. The second mechanism is independent of the absorber thickness showing EQE saturation already above 15 V. This is most likely related to crystal defects penetrating through the absorber layer and forming electrically active channels between the electrodes and the carrier collection volume.