Christie Simmons

Crystalline silicon photovoltaics: a cost analysis framework for determining technology pathways to reach baseload electricity costs

Crystalline silicon (c-Si) photovoltaics are robust, manufacturable, and Earth-abundant. However, barriers exist for c-Si modules to reach US

Room-temperature sub-band gap optoelectronic response of hyperdoped silicon

0.50–0.75/Wp fabrication costs necessary for subsidy-free utility-scale adoption. We evaluate the potential of c-Si photovoltaics to reach this goal by developing a bottom-up cost model for c-Si wafer, cell, and module manufacturing; performing a sensitivity analysis to determine research domains that provide the greatest impact on cost; and evaluating the cost-reduction potential of line-of-sight manufacturing innovation and scale, as well as advanced technology innovation. We identify research domains with large cost reduction potential, including improving efficiencies, improving silicon utilization, and streamlining manufacturing processes and equipment, and briefly review ongoing research and development activities that impact these research domains. We conclude that multiple technology pathways exist to enable US

High-fidelity resonant gating of a silicon-based quantum dot hybrid qubit

0.50/Wp module manufacturing in the United States with silicon absorbers. More broadly, this work presents a user-targeted research and development framework that prioritizes research needs based on market impact.

Picosecond carrier recombination dynamics in chalcogen-hyperdoped silicon

Room-temperature infrared sub-band gap photoresponse in silicon is of interest for telecommunications, imaging and solid-state energy conversion. Attempts to induce infrared response in silicon largely centred on combining the modification of its electronic structure via controlled defect formation (for example, vacancies and dislocations) with waveguide coupling, or integration with foreign materials. Impurity-mediated sub-band gap photoresponse in silicon is an alternative to these methods but it has only been studied at low temperature. Here we demonstrate impurity-mediated room-temperature sub-band gap photoresponse in single-crystal silicon-based planar photodiodes. A rapid and repeatable laser-based hyperdoping method incorporates supersaturated gold dopant concentrations on the order of 10(20) cm(-3) into a single-crystal surface layer ~150 nm thin. We demonstrate room-temperature silicon spectral response extending to wavelengths as long as 2,200 nm, with response increasing monotonically with supersaturated gold dopant concentration. This hyperdoping approach offers a possible path to tunable, broadband infrared imaging using silicon at room temperature.

Targeted Search for Effective Intermediate Band Solar Cell Materials

Isolated spins in semiconductors provide a promising platform to explore quantum mechanical coherence and develop engineered quantum systems. Silicon has attracted great interest as a host material for developing spin qubits because of its weak spin-orbit coupling and hyperfine interaction, and several architectures based on gate defined quantum dots have been proposed and demonstrated experimentally. Recently, a quantum dot hybrid qubit formed by three electrons in double quantum dot was proposed, and non-adiabatic pulsed-gate operation was implemented experimentally, demonstrating simple and fast electrical manipulations of spin states with a promising ratio of coherence time to manipulation time. However, the overall gate fidelity of the pulse-gated hybrid qubit is limited by relatively fast dephasing due to charge noise during one of the two required gate operations. Here we perform the first microwave-driven gate operations of a quantum dot hybrid qubit, avoiding entirely the regime in which it is most sensitive to charge noise. Resonant detuning modulation along with phase control of the microwaves enables a pi rotation time of less than 5 ns (50 ps) around X(Z)-axis with high fidelities > 93 (96) %. We also implement Hahn echo and Carr-Purcell (CP) dynamic decoupling sequences with which we demonstrate a coherence time of over 150 ns. We further discuss a pathway to improve gate fidelity to above 99 %, exceeding the threshold for surface code based quantum error correction.

The effect of embedded nanopillars on the built-in electric field of amorphous silicon p-i-n devices

Intermediate-band materials have the potential to be highly efficient solar cells and can be fabricated by incorporating ultrahigh concentrations of deep-level dopants. Direct measurements of the ultrafast carrier recombination processes under supersaturated dopant concentrations have not been previously conducted. Here, we use optical-pump/terahertz-probe measurements to study carrier recombination dynamics of chalcogen-hyperdoped silicon with sub-picosecond resolution. The recombination dynamics is described by two exponential decay time scales: a fast decay time scale ranges between 1 and 200 ps followed by a slow decay on the order of 1 ns. In contrast to the prior theoretical predictions, we find that the carrier lifetime decreases with increasing dopant concentration up to and above the insulator-to-metal transition. Evaluating the materials figure of merit reveals an optimum doping concentration for maximizing performance.

Hyperdoped silicon sub-band gap photoresponse for an intermediate band solar cell in silicon

Recent years have seen a number of candidate materials for intermediate band (IB) solar cells, but none has demonstrated a high-efficiency device. We explain this deficit by means of a figure of merit, which predicts the potential effectiveness of candidate IB materials in advance of device fabrication. This figure of merit captures in a single parameter the inherent tradeoff between enhanced absorption and enhanced recombination within an IB material, and it suggests a path toward efficient IB materials. We illustrate a screening approach based on this figure of merit for a specific class of IB material systems: a dopant-induced impurity band in silicon. We show, in this case, that the optical and nonradiative electrical trapping cross sections of impurities, widely studied properties that can be measured in bulk materials, determine the potential performance of IB solar cell devices. We conclude with a list of appealing and unappealing candidate material systems.

Decoupling surface- and bulk-limited lifetimes in 100-μm thin silicon using transient absorption pump-probe spectroscopy

In this work, we report on the experimental modification of the built-in electric field of a-Si:H p-i-n junctions, resulting from Agnanopillars embedded within the intrinsic layer (i-layer). Increased open-circuit voltages, from J-V traces, and reduced charge transit-times, from time-of-flight (ToF) measurements, indicate that the built-in electric field within the i-layer is increased with respect to unstructured reference samples. Decreased short-circuit current density values coupled with competing diode J-V characteristics, however, indicate that the charge collection from the i-layer is significantly decreased for the nanopillar samples. Theoretical and functional analysis of the ToF data reaffirms both reduced charge-transit times and decreased charge collection, and is able to quantitatively confirm the enhanced built-in electric field of the nanopillar samples.

Enhancing the Infrared Photoresponse of Silicon by Controlling the Fermi Level Location within an Impurity Band

Hyperdoping silicon with impurities is considered an attractive method to develop an intermediate band solar cell in silicon with the potential to increase the photovoltaic cell efficiency beyond that of the Shockley-Queisser limit by utilizing sub-band gap photons for energy generation. Unfortunately, to date sub-band gap photoresponse has not been observed in singlecrystal hyperdoped silicon at room temperature, which is crucial for the development of intermediate band solar cells. In this contribution, we report and analyze room-temperature sub-band gap photoresponse of single-crystal silicon hyperdoped with gold. We further discuss the potential of using gold-hyperdoped silicon for IBSC in silicon.

Hole-mobility-limiting atomic structures in hydrogenated amorphous silicon

The transient decay of excess photo-generated carriers in a 100-μm thin unpassivated crystalline Si (c-Si) wafer is measured using transient absorption pump-probe spectroscopy with two excitation wavelengths (750 nm and 1050 nm), based on the principle of free-carrier absorption. To decouple the bulk-and surface-limited lifetimes, we use state-of-the-art simulation software Sentaurus TCAD [1] to model the experimentally obtained decay characteristics of minority carrier densities. We show that by combining transient absorption pump-probe spectroscopy technique with TCAD simulations, reasonable bounds for both bulk and surface recombination parameters can be determined. The value obtained for the surface recombination velocity is consistent with literature and a lower limit for bulk lifetime can be obtained.