Very narrow SiGe/Si quantum wells deposited by low-temperature atmospheric pressure chemical vapor deposition

The optical, structural, and electrical properties of very narrow SiGe quantum wells grown by "ultra-clean" atmospheric pressure chemical vapor deposition (APCVD) are investigated. X-ray reflectivity data reveal abrupt interfaces with a root-mean-square roughness of not more than 0.2 nm. For the first time narrow (4.3 meV) excitonic photoluminescence (PL) spectra were obtained from APCVD grown samples containing SiGe wells with 12.5% to 32.5% Ge. For the narrowest wells PL doublets are observed which are attributed to atomic steps at the SiGe/Si interfaces. The PL and x-ray diffractometry data show that process deposition control for well and barrier width is within the monolayer range. Resonant tunneling diodes fabricated with 2.5-mm-wide Si0.75Ge0.25 wells show world record peak to valley ratios of 4.2. Magneto-transport measurements performed at high magnetic fields of two-dimensional hole gases exhibit pronounced Hall plateaus and well-defined Shubnikov de Hass oscillations, indicating high material quality. The results give evidence that atmospheric pressure chemical vapor deposition, which relies on gas switching sequences of the reactive gases in a hydrogen ambience, is able to produce interface abruptness comparable if not better than reported by any other technique.