Evolution of Photocurrent during Coadsorption of Cs and O on GaAs （100）

The photocurrent and spectral response characteristics of gallium arsenide （GaAs） are obtained by a multiinformation measurement system, and the evolution of the photocurrent versus the Cs：O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent.     

Current-voltage characteristics simulation and analysis of 4H-SiC metal-semiconductor-metal ultraviolet photodetectors

The current-voltage (Ⅰ-Ⅴ) characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet pho- todetector with different finger widths and spacings,different carrier concentrations and thicknesses of n-type epitaxial layer are simulated.The simulation results indicate that the dark current and the pho- tocurrent both increase when the finger width increases.But the effect of finger width on the dark current is more significant.On the other hand,the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases,the photocurrent decreases and the dark current is almost changeless. In addition,it is found that the smaller the carrier concentration of n-type epitaxial layer is,the smaller the dark current and the larger the photocurrent will be.It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness.The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3μm.     

Physical mechanism of two-photon response in semi-insulating GaAs

The physical mechanism of two-photon response （TPR） in semi-insulating GaAs is studied. The measured photocurrent generated from the fabricated hemispherical GaAs sample responding to 1.3μm continuous wave laser shows a quadratic dependence on the coupled optical power and no saturation with the bias. The angular dependence of the photocurrent on the azimuth is in agreement with the anisotropy of double-frequency absorption （DFA） in GaAs single crystals. These results demonstrate DFA is the dominant mechanism of TPR in GaAs.     

Gate-dependent photoresponse in self-assembled graphene p–n junctions

The intrinsic photocurrent generation mechanism of a self-assembled graphene p–n junction operating at 1.55 μm is investigated experimentally.It is concluded that both a photovoltage effect and a photothermoelectric effect contribute to the final photocurrent.The photocurrent signal at the p–n junction was found to be dominated by photothermoelectric current,arising from different self-assembled doping levels.     

Investigation of Chemical-Vapour-Deposition Dialnond Alpha-Particle Detectors

Diamond films with [100] texture were prepared by a hot-silament chemical vapour deposition technique to fabricate particale detectors.the response of detectors to 5.5MeV^241 am particles is studied.The photocurrent increases linearly and then levels off with voltage,and 7nA is obtained at bias voltage of 100V.The timedependent photocurrent initially increases rapidly and then tends to reach saturation.Furthermore,a little increase of the dark-current after irradiation can be accounted for by the release of the charges captured by the trapping centres at low energy levels during irradiation.An obvious peak of the pulse height distribution can be observed,associated with the energy of 5.5MeV.     

Spin Transport under In-plane Electric Fields with Different Orientations in Undoped InGaAs/AlGaAs Multiple Quantum Wells

The spin-polarized photocurrent is used to study the in-plane electric field dependent spin transport in undoped InGaAs/AlGaAs multiple quantum wells. In the temperature range of 77–297 K, the spin-polarized photocurrent shows an anisotropic spin transport under different oriented in-plane electric fields. We ascribe this characteristic to two dominant mechanisms: the hot phonon effect and the Rashba spin-orbit effect which is influenced by the in-plane electric fields with different orientations. The formulas are proposed to fit our experiments, suggesting a guide of potential applications and devices.     

Photovoltage analysis of a heterojunction solar cell

According to the p-n junction model of Shockley,the relationship between the equilibrium carrier concentrations of n-type and p-type semiconductors on the edges of the depletion region of a p-n junction solar cell is analysed.The calculation results show that the photovoltage can exceed the built-in voltage for a special kind of heterojunction solar cell.When the photovoltage exceeds the built-in voltage under illumination,the dark current and the photocurrent are impeded by the peak of voltage barrier at the interface and the expression of the total I-V characteristic is given.     

Carrier transport in III–V quantum-dot structures for solar cells or photodetectors

According to the well-established light-to-electricity conversion theory,resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent,which have been observed in quantum dots without a p–n junction at an external bias.Here,we experimentally observed more than 88% of the resonantly excited photo carriers escaping from In As quantum dots embedded in a short-circuited p–n junction to form photocurrent.The phenomenon cannot be explained by thermionic emission,tunneling process,and intermediate-band theories.A new mechanism is suggested that the photo carriers escape directly from the quantum dots to form photocurrent rather than relax to the ground state of quantum dots induced by a p–n junction.The finding is important for understanding the low-dimensional semiconductor physics and applications in solar cells and photodiode detectors.     

Enhanced photogalvanic effect in the two-dimensional MgCl2/ZnBr2 vertical heterojunction by inhomogenous tensile stress

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl₂/ZnBr₂ vertical van der Waals heterojunction with the noncentrosymmetric C_3v symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl₂/ZnBr₂ vertical heterojunction in the low-power UV photodetection.     

RCE photodiodes at wavelength band of 1.06

Resonant cavity enhancement (RCE) typed optical detector and modulator which operating at wavelength band of 1.06 μm is reported. The peak quantum efficiency of detector is reasonably high as 50% without bias, and the photocurrent contrast ratio of modulator is 3.6 times at -3.5 V as compared to 0 V. The incident angle dependence of RCE device's photoelectric response is investigated carefully.