Fabrication of Ge:Ga Hyperdoped Materials and Devices Using CMOS-Compatible Ga and Ge Hydride Chemistries.

We report a versatile chemical vapor deposition (CVD) method to dope Ge films with Ga atoms in situ over a wide concentration range spanning from 3 × 10 to 2.7 × 10 cm. The method introduces a stable and volatile Ga hydride [DGaN(CH)] that reacts readily with GeH to deliver Ga dopants controllably and systematically at complementary metal-oxide-semiconductor compatible ultralow temperatures of ∼360 °C. Thick and monocrystalline layers (1.3 μm) are produced on Si substrates at growth rates approaching 50 nm/min. The doped crystals are fully epitaxial and devoid of misfit defects and Ga precipitates as evidenced by Rutherford backscattering spectrometry, X-ray diffraction, and cross-sectional transmission electron microscopy. The Ga contents measured by secondary ion mass spectrometry and the active carrier concentrations determined by spectroscopic ellipsometry (as well as Hall effect measurements in several cases) are in close agreement, indicating near full activation. Photoluminescence spectra show a strong emission peak at 0.79 eV corresponding to the direct gap E transition, evidence of the indirect transition, and additional structures characteristic of p-type Ge. Electroluminescence and I- V curves measured from p(Ga)-i-n photodiodes are found to be at par with those from boron-based reference devices. These results are promising and demonstrate that a single-source CVD approach allows independent control of Ga doping level and junction depth, producing flat dopant profiles, high activation ratios, uniform distributions, and sharp interfaces. This method potentially represents a viable alternative to state-of-the-art boron-based p-type doping and activation of Ge-like materials.