Short-wavelength-infrared (SWIR; 1.4–3.0 µm) photodetection is important for various applications. Inducing a low-cost silicon-compatible material, such as germanium, to detect SWIR light would be advantageous for SWIR applications compared with using conventional (III-V or II-VI) SWIR materials. Here, we present a scalable nonequilibrium method for hyperdoping germanium with gold for dopant-mediated SWIR photodetection. Using ion implantation followed by nanosecond pulsed laser melting, we obtain a single-crystal material with a peak gold concentration of 3 × ${10}^{19}{\mathrm{cm}}^{-3}$ $({10}^3$ times the solubility limit). This hyperdoped germanium has fundamentally different optoelectronic properties from those of intrinsic and conventionally doped germanium. This material exhibits sub-band-gap absorption of light up to wavelengths of at least 3 µm, with a sub-band-gap optical absorption coefficient comparable to that of commercial SWIR photodetection materials. We show that germanium hyperdoped with gold exhibits sub-band-gap SWIR photodetection at room temperature, in contrast with previous doped-germanium photodetector studies, which only show a low-temperature response. This material is a potential pathway to low-cost room-temperature silicon-compatible SWIR photodetection.

Obtaining high level active n⁺ carrier concentrations in germanium (Ge) has been a significant challenge for further development of Ge devices. By ion implanting phosphorus (P) and fluorine (F) into Ge and restoring crystallinity using Nd:YAG nanosecond pulsed laser melting (PLM), we demonstrate 10²⁰ cm⁻³ n⁺ carrier concentration in tensile-strained epitaxial germanium-on-silicon. Scanning electron microscopy shows that after laser treatment, samples implanted with P have an ablated surface, whereas P + F co-implanted samples have good crystallinity and a smooth surface topography. We characterize P and F concentration depth profiles using secondary ion mass spectrometry and spreading resistance profiling. The peak carrier concentration, 10²⁰ cm⁻³ at 80 nm below the surface, coincides with the peak F concentration, illustrating the key role of F in increasing donor activation. Cross-sectional transmission electron microscopy of the co-implanted sample shows that the Ge epilayer region damaged during implantation is a single crystal after PLM. High-resolution X-ray diffraction and Raman spectroscopy measurements both indicate that the as-grown epitaxial layer strain is preserved after PLM. These results demonstrate that co-implantation and PLM can achieve the combination of n⁺ carrier concentration and strain in Ge epilayers necessary for next-generation, high-performance Ge-on-Si devices.

Obtaining short-wavelength-infrared (SWIR; 1.4 μm–3.0 μm) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 10²⁰ cm⁻³ (10⁴ times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 μm, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 μm from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors.

India is anticipated to grow its total energy consumption and CO₂ emissions by more than any other country over the next two decades. India will have to attract around $400 billion in financing to realize its 500 GW target of renewable energy by 2030. Given complex renewable energy sector risks, rapidly scaling-up risk-friendly private equity financing will be critical to achieve India's target. This research seeks to answer questions regarding the motivation, perceptions, strategies, and investment behavior of private equity investors in the Indian renewable energy sector. The answers to these questions presented herein have been distilled from primary research interviews with 40 executive-level sector practitioners and literature analysis. This research finds that global-macro forces and sector-specific appeal are attracting varied investors to the sector. These investors primarily deploy capital in existing developer platforms, creating control developer platforms, and Infrastructure Investment Trusts. Critical investment criteria and value creation strategies of these investors are comprehensively discussed. Emerging investment opportunities to create new renewable energy sector value by partnering with companies across the power sector value chain are also presented. This research concludes that despite significant sector risks, investors remain confident they can achieve outsized risk-adjusted returns relative to most other global infrastructure assets. This optimism stems from the confidence of investors in their own ability to manage risk-return dynamics through judicious investment selection and management strategies, the sector's uniquely large demand growth and market size, and the Indian central government's perceived strong commitment to finding creative solutions to chronic sector issues. Lessons from the investment insights, themes and factor analyses discussed herein can be drawn upon in evaluating renewable energy investments and policymaking worldwide.