Characterization of quantum well structures using surface photovoltage spectroscopy

Ashkenasy, Nurit; Leibovitch, M.; Rosenwaks, Y.; Shapira, Yoram

doi:10.1016/s0921-5107(99)00547-4

Cited by 7 publications

(5 citation statements)

References 38 publications

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“…It has been reported that the signal generated by the photovoltaic effect dominates for samples with a p-n junction. 21,22) Because the SL structure was embedded in the i region of the solar cell structure, we considered that the SPV signals below the E g of GaAs were caused by the photovoltaic signal related to the optical transition between the quantum levels in the SL region. In this case, photo-excited carriers in the quantum levels thermally escape to the potential barrier layer and accumulate at the sample surface owing to the built-in electric field in the i region.…”

Section: Resultsmentioning

confidence: 99%

“…Because SPV spectroscopy is a method for detecting a surface potential change by photo-generated carrier accumulation, it has been reported that the signal caused by a photovoltage effect is also observed in a sample with a p-n junction. 21,22) Moreover, electrode formation is not needed for the measurement. Therefore, a combination of PPT and SPV spectroscopies is useful for evaluating the performance in the initial stage of solar cell fabrication.…”

Section: Introductionmentioning

confidence: 99%

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Effects of barrier thickness on carrier non-radiative relaxation process in InGaAs/GaAsP superlattice solar cells by piezoelectric photothermal and surface photovoltage spectroscopies

Nakamura¹,

Fukuyama²,

Sugiyama³

et al. 2019

Jpn. J. Appl. Phys.

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We investigated the carrier non-radiative relaxation process of InGaAs/GaAsP superlattice (SL) solar cells with different barrier thicknesses by combining piezoelectric photothermal (PPT) and surface photovoltage (SPV) measurements. The former technique detected heat generated by non-radiative relaxation and the latter detected the surface potential change induced by the carrier accumulation. Although the mechanisms of these measurements were different, corresponding signals of the transition between the quantum levels were observed in both spectra. The SPV signal intensities were independent of the barrier thicknesses. The carrier tunneling process functioned poorly under open-circuit conditions. Conversely, the PPT signal intensities increased with decreasing barrier thickness. We experimentally demonstrated that the non-radiative relaxation component increased as the barrier thicknesses decreased owing to the lattice relaxation at interfaces between the quantum well and barrier layers. We concluded that the non-radiative relaxation process in the SL structure must be directly evaluated to improve the solar cell performance.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of barrier thickness on carrier non-radiative relaxation process in InGaAs/GaAsP superlattice solar cells by piezoelectric photothermal and surface photovoltage spectroscopies

Nakamura¹,

Fukuyama²,

Sugiyama³

et al. 2019

Jpn. J. Appl. Phys.

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“…The resonance wavelength of the vertical cavity structure was determined from SPVS, where the photo-voltage induced by light incident on the surface of the wafer is measured [32][33][34]. A sharp peak in the photo-voltage is seen at the cavity resonance wavelength due to a higher photon density, within the vertical cavity, increasing the number of electron-hole pairs generated at the active region.…”

Section: Methodsmentioning

confidence: 99%

Gain measurements on VCSEL material using segmented contact technique

Hentschel

Allford²,

Gillgrass³

et al. 2023

J. Phys. D: Appl. Phys.

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We report direct measurements of the optical gain on vertical-cavity surface-emitting laser (VCSEL) material using a stripe-length method featuring segmented contacts. We utilise the similarity of the in-plane transverse electric (TE) polarised matrix element and that of the VCSEL lasing mode and a simple method to reduce round trip effects. The confinement factor is determined from cold-cavity simulations of the in-plane TE polarised slab waveguide mode and used to convert the measured in-plane modal gain into the vertical-cavity modal gain, as required for the VCSEL structure. This gives a threshold material gain of 1440 ± 140 cm−1 at 30 °C for this structure. A comparison with the threshold material gain values determined from the lasing condition, where internal optical losses due to doping induced absorption is included using parameters taken from the literature, indicates the presence of an additional source of optical loss in the experiment which increases the threshold material gain by ∼450 cm−1. A best fit is obtained by increasing the optical loss in the n-DBR (distributed Bragg reflectors) layers to 40 cm−1, which is consistent with previous work on additional scattering losses due to interface roughening in the n-DBR layers. To further demonstrate the utility of this method for rapid optimisation, the gain-peak wavelength is measured directly, and its temperature dependence is compared to the lasing wavelength.

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“…More time-consuming measurements, such as wavelength variation with current and temperature, were performed on a reduced number of devices based on L-I-V-λ screening. Additionally, surface photovoltage spectroscopy (SPVS) [31][32][33] was used to Fabrication followed common processing techniques which, for the standard VCSEL structures was as follows: definition of the mesa by inductively coupled plasma (ICP) etch to just below the active layers, a depth of ~3 µm. Wet thermal oxidation of the samples at 400 • C to form the oxide apertures with an oxidation depth of 5.5 ± 0.5 µm.…”

Section: Methodsmentioning

confidence: 99%

“…More time-consuming measurements, such as wavelength variation with current and temperature, were performed on a reduced number of devices based on L-I-V-λ screening. Additionally, surface photovoltage spectroscopy (SPVS) [31][32][33] was used to measure the cavity mode wavelength of the epi-material. SPVS involves shining wavelength-varied monochromatic light normal to the surface of the sample and measuring the voltage induced as photogenerated electron-hole pairs are separated by the built-in field.…”

Section: Methodsmentioning

confidence: 99%

Quick Fabrication VCSELs for Characterisation of Epitaxial Material

et al. 2021

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A systematic analysis of the performance of VCSELs, fabricated with a decreasing number of structural elements, is used to assess the complexity of fabrication (and therefore time) required to obtain sufficient information on epitaxial wafer suitability. Initially, sub-mA threshold current VCSEL devices are produced on AlGaAs-based material, designed for 940 nm emission, using processing methods widely employed in industry. From there, stripped-back Quick Fabrication (QF) devices, based on a bridge-mesa design, are fabricated and this negates the need for benzocyclcobutane (BCB) planarisation. Devices are produced with three variations on the QF design, to characterise the impact on laser performance from removing time-consuming process steps, including wet thermal oxidation and mechanical lapping used to reduce substrate thickness. An increase in threshold current of 1.5 mA for oxidised QF devices, relative to the standard VCSELs, and a further increase of 1.9 mA for unoxidised QF devices are observed, which is a result of leakage current. The tuning of the emission wavelength with current increases by ~0.1 nm/mA for a VCSEL with a 16 μm diameter mesa when the substrate is unlapped, which is ascribed to the increased thermal resistance. Generally, relative to the standard VCSELs, the QF methods employed do not significantly impact the threshold lasing wavelength and the differences in mean wavelengths of the device types that are observed are attributed to variation in cavity resonance with spatial position across the wafer, as determined by photovoltage spectroscopy measurements.

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Characterization of quantum well structures using surface photovoltage spectroscopy

Cited by 7 publications

References 38 publications

Effects of barrier thickness on carrier non-radiative relaxation process in InGaAs/GaAsP superlattice solar cells by piezoelectric photothermal and surface photovoltage spectroscopies

Effects of barrier thickness on carrier non-radiative relaxation process in InGaAs/GaAsP superlattice solar cells by piezoelectric photothermal and surface photovoltage spectroscopies

Gain measurements on VCSEL material using segmented contact technique

Quick Fabrication VCSELs for Characterisation of Epitaxial Material

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