Regensburg 2004 – scientific programme

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DS: Dünne Schichten

DS 22: Postersitzung

DS 22.54: Poster

Tuesday, March 9, 2004, 14:30–17:00, Poster B

Majority-carrier properties of low-temperature epitaxial Si — •S. Brehme, U. Knipper, B. Rau, and W. Fuhs — Hahn-Meitner-Institut Kékulestr. 5 12489 Berlin

In this contribution we report the results of electrical investigations on thin Si films grown epitaxial at temperatures below 600 ^∘C. Such films are possible candidates for absorber layers in thin-film solar cells on glass. Films were grown by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) on Si substrates. n- and p-type wafers of varying conductivity were used in the same run to render possible different types of electrical measurements such as capacitance voltage (CV), Hall effect (HE), and Deep Level Transient Spectroscopy (DLTS). The nominally undoped thin films were found to have room temperature electron concentrations in the range 10¹⁶ cm⁻³ to 10¹⁷ cm⁻³ depending on certain details of the growth process. From CV measurements similar results were obtained. Hall mobilities in the range 400 to 700 cm²/Vs were observed. Considering the ratio R of experimentally observed mobilities to values in a Si wafer of the same doping level, R values of typical 50 % are found in thin films with doping levels N_d of about 1 × 10¹⁶ cm⁻³. For layers with higher N_d R increases indicating different degrees of compensation. DLTS measurements show the presence of several electron-emitting trap levels with a dominant peak P1 at E_C - 0.27 eV. Concentrations of P1 of some 10¹⁴ cm⁻³ were determined from peak heights. Since the peaks of all the observed traps were broadened, real concentration values are still higher. Nevertheless, shallow levels dominate the conductivity. That is further approved by HE measurements down to 25 K.