The formation of GaAs/Si photodiodes by pulsed-laser deposition

摘要

Hetero-pairing of thin-film GaAs on Si is of considerable interest for novel applications in optoelectronics. However, the formation of high-quality GaAs is difficult and requires expensive top technologies such as molecular beam epitaxy (MBE) and related methods. In general, MBE forms high-quality epitaxial layers but is not capable of the straightforward formation of GaAs on Si because of the 4.1% lattice mismatch between both materials. We have developed and explored the possibilities of pulsed-laser deposition (PLD) for the formation of GaAs films on (100) n-type Si substrates. The films have been produced in vacuum (10~(-6) torr) employing the fundamental (1064 nm), second (532 nm), and third (355 nm) harmonic emission of a Nd: YAG laser with a repetition rate of 10 Hz and a pulse duration of 6 ns. The laser was focused on (100) p-type (10~(19) cm~(-3)) GaAs wafers with an energy fluence of 0.79-0.84 J/cm~2. During the deposition, the substrate was not heated. The current-voltage characteristic of the samples showed rectification, i.e., the doping of the GaAs target was successfully maintained in the PLD film and a diode was formed in conjunction with the oppositely doped Si substrate. The observation of photocurrent without bias is an additional proof that an operating junction was achieved. The crystallographic quality of the films was checked by x-ray analysis and revealed that the films show [111]-oriented crystalline parts. The realization of GaAs/Si photodiodes reveals the potential of PLD to be used for the monolithic integration of GaAs photonic devices with Si circuits.