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Ge/Si heterostructure diodes based on n^++Si(100)/i\-Ge/p\-Ge and p^++Si(100)/i\-Ge/n\-Ge stacks and intrinsic region thickness of \sim350 and \sim900~nm, respectively, were fabricated using a specially developed synthesis protocol that allows unprecedented control of film microstructure, morphology, and purity at complementary metal–oxide–semiconductor compatible conditions. From a growth and doping perspective, a main advantage of our inherently low-temperature (390^\circC) soft-chemistry approach is that all high-energy processing steps are circumvented. Current–voltage measurements of circular mesas (60–250 \mum in diameter) show dark current densities as low as 6 \times 10^-3~A/cm^2 at -1~V bias, which is clearly improved over devices fabricated under low thermal budgets using traditional Ge deposition techniques. Spectral photocurrent measurements indicate external quantum efficiencies between 30 and 60% of the maximum theoretical value at zero bias, and approaching full collection efficiency at high reverse biases. The above Ge devices are compared to analogous low-temperature-grown (350^\circC) Ge{0.98}Sn0.02 diodes. The latter display much higher dark currents but also higher collection efficiencies close to 70% at zero bias. Moreover, the quantum efficiency of these Ge0.98Sn0.02 diodes remains strong at wavelengths longer than 1550 nm out to 1750 nm due to the reduced band gap of the alloy relative to Ge. [ABSTRACT FROM PUBLISHER]

Ge–Si based n-type films are synthesized using specially designed hydrides P(SiH3)3, Ge3H8 and Ge4H10 for potential applications in next-generation CMOS technologies. The films are grown on Ge buffered Si(100) at 340 °C using two complementary methods. The first employs a gas-source molecular epitaxy approach using Ge4H10 to produce materials with P doping densities varying from 4 × 1018 to a 3.5 × 1019 cm−3 threshold. These materials are co-doped with Si concentrations ranging from 3 × 1019 cm−3 to 3.5%, roughly in proportion with the amount of P(SiH3)3 used in the reactions. The second approach applies an alternative ultra-high vacuum chemical vapor deposition (UHV–CVD) technique and Ge3H8 in place of Ge4H10 to achieve ultra-high carrier concentrations up to ∼6 × 1019 cm−3. The Si content in this case is minimal—in the 2–6 × 1019 cm−3 range—indicating that the growth mechanism allows only ‘impurity’ levels of Si to be incorporated. The active carrier densities in both cases closely reflect the absolute P content, indicating that the P atoms are mostly substitutional. The electron mobilities are significantly higher compared to state-of-the-art prototypes, probably due to superior microstructure and dearth of inactive donors in the lattice. P–I–N diodes fabricated using the P(SiH3)3 compound show I–V characteristics comparable to state-of-the-art results for Ge-on-Si devices and are virtually undistinguishable from similar diodes doped with the P(GeH3)3 precursor. These results confirm P(SiH3)3 as a viable CVD doping source that is practical from a process standpoint and therefore attractive for industrial scale-up. [ABSTRACT FROM AUTHOR]