Contactless Microwave Measurements of Photoconductivity in Silicon Hyperdoped with Chalcogens

Abstract

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Methodology for vetting heavily doped semiconductors for intermediate band photovoltaics: A case study in sulfur-hyperdoped silicon

“…(9) represents an upper limit on the l e s e product because we cannot rule out the possibility that additional artifacts, such as internal photoemission from the contacts, contribute to the response. The value of this sub-band gap response is consistent with the previous contactless measurements, 33 and provides an upper limit that is nearly two orders of magnitude lower than the previous room temperature measurements. 29 It is important to note that carrier lifetimes are expected to be much higher at lower temperatures (a decreased thermal velocity v th e and decreased capture cross-section 60 leads to higher lifetimes) and thus the figure of merit at room temperature is expected be lower than the value measured here.…”

“…3,4,18 In this article, we will focus on the latter concept, which has been studied extensively from a materials standpoint in two primary material systems: silicon hyperdoped with Ti (Si:Ti) [19][20][21][22][23][24][25][26] and silicon hyperdoped with sulfur (Si:S). [27][28][29][30][31][32][33][34][35] Despite significant efforts on these impurity-band materials, no high-efficiency devices have been demonstrated. We present an experimental framework that predicts whether a candidate impurity-band material system will actually enhance the efficiency of a photovoltaic (PV) device.…”

“…Previous room-temperature photoconductivity measurements of Si:S did not produce detectable photoresponse, 33 allowing researchers to place an upper limit on l e s e of 1 Â 10 À7 cm 2 /V, based on the noise floor of the measurement. 29 However, this value of l e s e is consistent with e greater than or less than 1 for Si:S. Thus, it is not possible to draw a conclusion about the efficiency potential of Si:S from this previous bound.…”

Picosecond carrier recombination dynamics in chalcogen-hyperdoped silicon

“…13 Microwave photoconductivity decay and low-temperature photoconductivity measurements on carrier dynamics in this material lack the time-resolution required to measure the lifetime directly. [14][15][16] Similar to microwaves, THz radiation is long-wavelength electromagnetic radiation and is sensitive to free charge carriers. Moreover, subpicosecond-duration THz pulses can be straightforwardly generated, enabling direct mapping of the carrier recombination dynamics on picosecond time scales.…”

Effect of layer thickness on device response of silicon heavily supersaturated with sulfur

“…7 The optoelectronic properties of the Il-PLM material have been studied as well. 8,9 Relatively less work has been done on the above-band gap optoelectronic properties of this material, in part because the strong contribution to the absorption made by the substrate makes isolation of the II-PLM layer challenging. Recently, a careful experimental investigation used the II-PLM method to incorporate S into the device layer of a silicon-on-insulator (SOI) wafer, and then chemically etched a "window" in the handle wafer to permit measurement of the S-doped layer without the substrate.…”