Hamburg 2001 – scientific programme

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HL: Halbleiterphysik

HL 7: Poster I

HL 7.2: Poster

Monday, March 26, 2001, 10:30–19:00, Rang S\ 3

Fabrication of vertical SiGe MSM photodetectors for mid-IR radiation — •Dan Buca¹, Stephan Winnerl¹, Christoph Buchal¹, and Dan-Xia Xu² — ¹Institut für Schichten und Grenzflächen (ISG-IT), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany — ²National Research Council, Ottawa, Ontario KIA OR6, Canada

We report on the fabrication and dc characterization of vertical SiGe MSM (metal-semiconductor-metal) photodetectors. The devices are manufactured on single crystalline CoSi₂ layers made by implantation into Si (100) wafers. They consist of a molecular beam epitaxy (MBE) grown 120 nm thick Si buffer layer, 10 periods of 5 nm thick SiGe with 12 nm thick Si undulating quantum wells and a Si cap layer of 90 nm. We used 50% Ge concentration in the SiGe multiquantum well (MQW) in order to obtain a band gap energy lower than 800 meV for photon detection at λ=1.55µm. The Si/Si_.5Ge_.5/Si stack is sandwiched between a thin top Cr layer (upper contact) and the buried CoSi₂ layer (lower contact), forming a double junction Schottky diode. The measurements show that the Schottky barrier height (SBH) for holes is 0.39-0.44 V at the CoSi₂ contact. At the Cr side the measured SBH is 0.47-0.495 V. The observed barrier height is slightly lowered by defects. We find threading dislocations with a density of 10⁶ cm⁻² at the Si/Si_.5Ge_.5 interfaces. Our design has the advantage of a low dark current due to the good Schottky contacts of Cr and CoSi₂ on Si and is intended to optimize the temporal response by using high mobility carriers within a strong homogeneous electrical field. Infrared absorption is possible due to the high Ge concentration.