“…A constant growth rate of 0.127 μmh −1 , calibrated using reflection high-energy electron diffraction, was used across the entire sample. More detailed information on the recent growth of GaAsBi in this system is reported elsewhere 36 .Figure 1 (a) Schematic diagram of the bulk GaAsBi sample studied in this work, grown via MBE. Representative temperature dependent PL spectra measured at (b) 666.4 Wcm −2
(c) 66.6 Wcm −2 and (d) 13.3 Wcm −2 .…”
A comprehensive assessment of the nature of the distribution of sub band-gap energy states in bulk GaAsBi is presented using power and temperature dependent photoluminescence spectroscopy. The observation of a characteristic red-blue-red shift in the peak luminescence energy indicates the presence of short-range alloy disorder in the material. A decrease in the carrier localisation energy demonstrates the strong excitation power dependence of localised state behaviour and is attributed to the filling of energy states furthest from the valence band edge. Analysis of the photoluminescence lineshape at low temperature presents strong evidence for a Gaussian distribution of localised states that extends from the valence band edge. Furthermore, a rate model is employed to understand the non-uniform thermal quenching of the photoluminescence and indicates the presence of two Gaussian-like distributions making up the density of localised states. These components are attributed to the presence of microscopic fluctuations in Bi content, due to short-range alloy disorder across the GaAsBi layer, and the formation of Bi related point defects, resulting from low temperature growth.
“…A constant growth rate of 0.127 μmh −1 , calibrated using reflection high-energy electron diffraction, was used across the entire sample. More detailed information on the recent growth of GaAsBi in this system is reported elsewhere 36 .Figure 1 (a) Schematic diagram of the bulk GaAsBi sample studied in this work, grown via MBE. Representative temperature dependent PL spectra measured at (b) 666.4 Wcm −2
(c) 66.6 Wcm −2 and (d) 13.3 Wcm −2 .…”
A comprehensive assessment of the nature of the distribution of sub band-gap energy states in bulk GaAsBi is presented using power and temperature dependent photoluminescence spectroscopy. The observation of a characteristic red-blue-red shift in the peak luminescence energy indicates the presence of short-range alloy disorder in the material. A decrease in the carrier localisation energy demonstrates the strong excitation power dependence of localised state behaviour and is attributed to the filling of energy states furthest from the valence band edge. Analysis of the photoluminescence lineshape at low temperature presents strong evidence for a Gaussian distribution of localised states that extends from the valence band edge. Furthermore, a rate model is employed to understand the non-uniform thermal quenching of the photoluminescence and indicates the presence of two Gaussian-like distributions making up the density of localised states. These components are attributed to the presence of microscopic fluctuations in Bi content, due to short-range alloy disorder across the GaAsBi layer, and the formation of Bi related point defects, resulting from low temperature growth.
“…Following the GaAsBi region growth, the growth temperature was raised to approximately 580 • C during another 20 min growth pause for growth of the Be doped GaAs capping layers. This means that the GaAsBi regions experienced an in situ anneal at 580 • C for approximately 1 h. More detailed information on sample growth and estimated Bi contents can be accessed elsewhere [18]. Following growth, the diodes were fabricated into circular mesa devices of several radii up to 200 µm using standard photolithography techniques and wet etching.…”
Section: Methodsmentioning
confidence: 99%
“…There have been relatively few reports of GaAsBi based diode dark current characteristics [3,[12][13][14][15][16][17][18][19] despite this being a key aspect of device performance. For reference, there have also been some reports of the dark currents observed in devices containing other dilute bismide materials: InAsBi [20], GaSbBi [21], and InGaAsBi [22].…”
The dark current characteristics of two series of bulk GaAsBi p-i-n diodes are analysed as functions of temperature and band gap. Each temperature dependent measurement indicates that recombination current dominates in these devices. The band gap dependence of the dark currents is also consistent with recombination dominated current for the devices grown at a common growth temperature, indicating that the presence of Bi does not directly adversely affect the dark currents. However, the devices grown at different growth temperatures exhibit a faster increase in dark current with decreasing device band gap, suggesting that a reduced growth temperature causes a reduction in minority carrier lifetime.
“…The temperature was then lowered for deposition of a 100 nm InGaAsBi layer, at the temperatures specified in table 1. Prior to the growth of the InGaAsBi layer the surface was exposed to a bismuth flux for 30s to soak the surface with bismuth, which was intended to increase bismuth incorporation as previously demonstrated for GaAsBi growth [15,16]. The InGaAsBi layer was grown using the same indium and gallium fluxes as used for the buffer layer, with a reduced As 2 BEP of (3.0±0.1) x 10 -6 mbar (As 2 :III ratio of 7.9:1) for all samples to allow bismuth incorporation into the layer while avoiding arsenic deficiency during growth (which would lead to a poor surface morphology).…”
Section: Ingaasbi Samples and Preliminary Characterisation Using Xrd mentioning
In this work we used a combination of photoluminescence (PL), high resolution X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) techniques to investigate material quality and structural properties of MBE-grown InGaAsBi samples (with and without an InGaAs cap layer) with targeted bismuth composition in the 3-4% range. XRD data showed that the InGaAsBi layers are more homogenous in the uncapped samples. For the capped samples, the growth of the InGaAs capped layer at higher temperature affects the quality of the InGaAsBi layer and bismuth distribution in the growth direction. Low temperature PL exhibited multiple emission peaks; the peak energies, widths and relative intensities were used for comparative analysis of the data in line with the XRD and RBS results. RBS data at random orientation together with channelled measurements allowed both an estimation of the bismuth composition as well as analysis of the structural properties. The RBS channelling showed evidence of higher strain due to possible anti-site defects in the capped samples grown at a higher temperature. It is also suggested that the growth of the capped layer at high temperature causes deterioration of the bismuth-layer quality. The RBS analysis demonstrated evidence of a reduction of homogeneity of uncapped InGaAsBi layers with increasing bismuth concentration. The uncapped higher bismuth concentration sample showed less defined channelling dips suggesting poorer crystal quality and clustering of bismuth on the sample surface.
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