Effective interface state effects in hydrogenated amorphous-crystalline silicon heterostructures using ultraviolet laser photocarrier radiometry

Abstract

Ultraviolet photocarrier radiometry (UV-PCR) was used for the characterization of thin-film (nanolayer) intrinsic hydrogenated amorphous silicon (i-a-Si:H) on c-Si. The small absorption depth (approximately 10 nm at 355 nm laser excitation) leads to strong influence of the nanolayer parameters on the propagation and recombination of the photocarrier density wave (CDW) within the layer and the substrate. A theoretical PCR model including the presence of effective interface carrier traps was developed and used to evaluate the transport parameters of the substrate c-Si as well as those of the i-a-Si:H nanolayer. Unlike conventional optoelectronic characterization methods such as photoconductance, photovoltage, and photoluminescence, UV-PCR can be applied to more complete quantitative characterization of a-Si:H/c-Si heterojunction solar cells, including transport properties and defect structures. The quantitative results elucidate the strong effect of a front-surface passivating nanolayer on the transport properties of the entire structure as the result of effective a-Si:H/c-Si interface trap neutralization through occupation. A further dramatic improvement of those properties with the addition of a back-surface passivating nanolayer is observed and interpreted as the result of the interaction of the increased excess bulk CDW with, and more complete occupation and neutralization of, effective front interface traps. V

Quantitative Imaging of Defect Distributions in CdZnTe Wafers Using Combined Deep-Level Photothermal Spectroscopy, Photocarrier Radiometry, and Lock-In Carrierography

“…Rapidly growing applications of CdZnTe as a material suitable for X-ray and γ-ray detector fabrication − and for high-efficiency solar cells , have introduced the urgent need for characterization of photocarrier properties and their associated solid-state transport parameters, including their spatial distributions in wafer substrates, which affect charge transport and limit the performance of optoelectronic devices. Most popular diagnostic methods in use are current deep-level transient spectroscopy (I-DLTS), transient current technique (TCT), current and capacitance vs voltage ( I – V and C – V ) measurements, γ-ray spectroscopy, Hall measurements, and optical and thermal measurements. − Beyond those methodologies, photocarrier radiometry (PCR) is a nondestructive and noncontacting spectrally gated frequency-domain dynamic semiconductor photoluminescence (PL) diagnostic modality, which allows for the simultaneous nondestructive determination of electronic transport parameters in semiconductor substrates and devices. − Subsequently, lock-in carrierography (LIC) was introduced as a near-infrared (NIR) imaging extension of PCR, aimed at constructing quantitative images of carrier transport parameters. − Next, two-beam heterodyne LIC (HeLIC) was introduced to address the need for high-frequency photocarrier excitation, eliciting fast enough signal responses required to measure short recombination lifetimes and other fast photocarrier relaxation processes. HeLIC was developed to allow high-frequency dynamic imaging of optoelectronic material and device properties, which require sampling rates orders of magnitude higher than those achievable by the frame rates of today’s fastest NIR camera technologies. − Very recently, heterodyne PCR (HePCR) proved to be very sensitive to photocarrier emission/capture processes out of, and into, band-gap defect and impurity states: a newly discovered HePCR phenomenon giving rise to a frequency-domain heterodyne signal amplitude depression (“dip” or “notch”) accompanied by a 180° phase transition was attributed to a nonlinear kinetic mechanism of laser-excited harmonic carrier density waves (CDW) interacting with trap or defect states in Si wafers .…”

Simultaneous determination of effective carrier lifetime and resistivity of Si wafers using the nonlinear nature of photocarrier radiometric signals

“…Photocarrier radiometry (PCR) [16] and its imaging counter part lock-in carrierography [17], a frequency-domain (FD) photoluminescence (PL) based quantitative characterization technique that measures photocarrier density distributions, has been demonstrated to be capable of characterizing carrier recombination properties [18][19][20], mobility/diffusivity [21,22], ion implantation dose [23], junction properties [24,25], and trap states/activation energy [26,27] in various semiconductor materials and devices. However, PCR shares the same nonlinearity issues as other dynamic optical techniques, which may substantially compromise its theoretical rigor and measurement self-consistency and reliability.…”