Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100−x Nanorods

We report the electrical and optical studies of thin films of a-GaxSe100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-GaxSe100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-GaxSe100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ0) is of the order of 101 Ω−1 cm−1, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration

Investigations on the physical origin of lateral photovoltage in PbS-colloidal quantum dot/Si heterojunctions

Restricted area heterojunctions, an array of lead sulfide colloidal quantum dots (PbS-CQDs) and crystalline silicon, are studied with a non-destructive remote contact light beam induced current (RC-LBIC) technique. As well as getting good quality active area images we observed an anomalous unipolar signal response for the PbS-CQD/n-Si devices and a conventionally expected bipolar signal profile for the PbS-CQD/p-Si devices. Interestingly, our simulation results consistently yielded a unipolar and bipolar nature in the signals related to the PbSCQD/n-Si and PbS-CQD/p-Si heterostructures, respectively. In order to explain the physical mechanism involved in the unipolar signal response of the PbS-CQD/n-Si devices, we propose a model based on the band alignment in the heterojunctions, in addition to the distribution of photo-induced excess majority carriers across the junction. Given that the RC-LBIC technique is well suited to this context, the presence of these two distinct mechanisms (the bipolar and unipolar nature of the signals) needs to be considered in order to have a better interpretation of the data in the characterization of an array of homo/heterojunctions

Optical absorption and photoluminescence studies on heavily doped (Ga,Mn)Sb crystals

Ga1-xMnxSb crystals are grown with different Mn doping concentrations by the horizontal Bridgman method (x = 0 - 0.04). Optical absorption and photoluminescence studies are carried out in the temperature range 3-300 K. Optical absorption studies reveal that the inter-valence band transition from the spin-orbit split-off band to the light/heavy hole bands is dominant over the fundamental valence band to conduction band absorption. In higher doped crystals, the fundamental absorption peak is merged with the inter-valence band transition and could not be resolved. Photoluminescence measurements in heavily doped crystals reveal the band gap narrowing and band filling effects due to the Fermi level shifting into the valence band

Effect of barrier thickness on structural, optical, and spectral behaviors of vertically strain coupled InAs/GaAs quantum dot infrared photodetectors

The optical, electrical, and spectral properties of a strain coupled InAs quantum dot detector with a fixed quaternary capping of InAlGaAs and variable GaAs barrier thickness were investigated along with an equivalent uncoupled structure. Self-assembled quantum dots with a multimodal dot size distribution were achieved owing to vertical strain coupling. Strain and electronic coupling were utilized to improve the optical and electrical performance of the fabricated quantum dot infrared photodetector. The peak spectral response was tuned by varying barrier thickness, and a blue shift (almost 1 mu m) was observed by increasing the capping thickness from sample A (90 angstrom capping) to E (500 angstrom capping). High responsivity and detectivity (similar to 10(10) cm Hz(1/2)W) were observed for all coupled samples as compared to the uncoupled sample. All coupled samples showed high thermal stability in the photoluminescence peak with high-temperature annealing. (C) 2014 American Vacuum Society

Comparison of Three Design Architectures for Quantum Dot Infrared Photodetectors: InGaAs-Capped Dots, Dots-in-a-Well, and Submonolayer Quantum Dots

In this letter, we compare three design architectures for quantum dot infrared photodetectors-InGaAs-capped InAs dots, InAs dot-in-a-well (DWELL), and InAs submonolayer (SML) heterostructures-in terms of optical and spectral behavior. The photoluminescence (PL) intensity measured of the SML sample at 8 K was 20 times stronger than that of the other samples, and its full-width at half-maximum value broader than the rest. Activation energy was calculated using temperature-dependent PL and dark current measurements, which showed the same trend. Peak spectral responses for the InGaAs-capped InAs dot and DWELL samples were observed at 4.1 and 7.3 mu m and at 4.1 and 8.5 mu m, respectively; however, only a single transition was observed for the SML sample because of the absence of a wetting layer. Spectral response of DWELL sample exhibited bias tunability at 87 K, and the SML sample exhibited high temperature of operation till 110 K. One order increment in responsivity was observed in the SML sample compared to others. The peak detectivity of InGaAs-capped InAs dot, DWELL, and SML samples was 4.1 x 10(9), 4.99 x 10(9), and 3.89 x 10(9) Jones, respectively, at 87 K