Amorphous Silicon 16—bit Array Photodetector

Abstract: An amorphous silicon 16 - bit array photodetector with the a - SiC/a -Si heterojunction diode is presented. The fabrication processes of the device were studied systematically. By the optimum of the diode structure and the preparation procedures, the diode with Id< 10 -12 A/mm2 and photocurrent Ip^0.35 A/W has been obtained at the wavelength of 632 nm.

Efficiency analysis of a-SiC:H thin film light emitting diodes

The hole injection,the radiative recombination and the device luminescent efficiencies of amorphous silicon carbide thin film p-i-n junction light emitting diodes are quantitatively calculated,and the effect of the carrier(especially the hole) injection and recombination processes on the device luminescent characteristics are revealed.Without considering the device junction temperature,it is found that the device luminescent efficiency mainly depends on the hole injection efficiency at low field and the hole radiative recombination efficiency at high field respectively.The theoretical analyses are in well agreement with the experimental results.

Theoretical investigation of optical properties and band gap engineering for Zn1-xTMxTe(TM=Fe,Co)alloys by modified Becke-Johnson potential

The direct band gap ZnTe with transition metal （TM） impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson （mBJ） functional for performing the structural computations and detailed investigations of the optical characters in Zn1_xTMxTe （TM = Fe, Co） alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn1_xTMxTe （TM = Fe, Co） have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.

Analytical Model for Calculating Trapped Charge in a－Si：H and Its Relative Error Analysis

Using a Taylor series expansion for the Fermi-Dirac occupation function,an accurate analytical model is developed for calculating the trapped-charge density in a-Si: H considering deep and tail states simultaneously without simplification.This is followed by the investigation of the relative errors of the localized trapped charge density in a-Si:H at all temperatures as a function of the quasi-Fermi level in the band gap calculated from three published analytical models and our above model. The results suggest that the relative errors of all these models increase notably as Efn is very closed to Ec(e.g.,-0.01 eV< Efn-Ec).It is also noticed that the relative errors of all above models become larger normally the greater is the value of temperature.A detailed analysis indicates that each model has its own applicability with various temperatures and various positions of the Fermi level.

Artificial optoelectronic synapse based on spatiotemporal irradiation to source-sharing circuitry of synaptic phototransistors

To overcome the intrinsic inefficiency of the von Neumann architecture,neuromorphic devices that perform analog vector–matrix multiplication have been highlighted for achieving power-and time-efficient data processing.In particular,artificial synapses,of which conductance should be programmed to represent the synaptic weights of the artificial neural network,have been intensively researched to realize neuromorphic devices.Here,inspired by excitatory and inhibitory synapses,we develop an artificial optoelectronic synapse that shows both potentiation and depression characteristics triggered only by optical inputs.The design of the artificial optoelectronic synapse,in which excitatory and inhibitory synaptic phototransistors are serially connected,enables these characteristics by spatiotemporally irradiating the phototransistor channels with optical pulses.Furthermore,a negative synaptic weight can be realized without the need for electronic components such as comparators.With such attributes,the artificial optoelectronic synapse is demonstrated to classify three digits with a high recognition rate(98.3%)and perform image preprocessing via analog vector-matrix multiplication.

Effect of active layer deposition temperature on the performance of sputtered amorphous In–Ga–Zn–O thin film transistors

The effect of active layer deposition temperature on the electrical performance of amorphous InGaZnO （a-IGZO） thin film transistors （TFTs） is investigated. With increasing annealing temperature, TFT performance is firstly improved and then degraded generally. Here TFTs with best performance defined as ＂optimized-annealed＂ are selected to study the effect of active layer deposition temperature. The field effect mobility reaches maximum at deposition temperature of 150℃ while the room-temperature fabricated device shows the best subthreshold swing and off-current. From Hall measurement results, the carrier concentration is much higher for intentional heated a-IGZO films, which may account for the high off-current in the corresponding TFT devices. XPS characterization results also reveal that deposition temperature affects the atomic ratio and Ols spectra apparently. Importantly, the variation of field effect mobility of a-IGZO TFTs with deposition temperature does not coincide with the tendencies in Hall mobility of a-IGZO thin films, Based on the further analysis of the experimental results on a-IGZO thin films and the corresponding TFT devices, the trap states at front channel interface rather than IGZO bulk layer properties may be mainly responsible for the variations of field effect mobility and subthreshold swing with IGZO deposition temperature.

The influence of RF power on the electrical properties of sputtered amorphous InGa-Zn-O thin films and devices

The influence of radio frequency（RF） power on the properties of magnetron sputtered amorphous indium gallium zinc oxide（a-IGZO） thin films and the related thin-film transistor（TFT） devices is investigated comprehensively.A series of a-IGZO thin films prepared with magnetron sputtering at various RF powers are examined.The results prove that the deposition rate sensitively depends on RF power.In addition,the carrier concentration increases from 0.91 x 1019 to 2.15 x 1019 cm-3 with the RF power rising from 40 to 80 W,which may account for the corresponding decrease in the resistivity of the a-IGZO thin films.No evident impacts of RF power are observed on the surface roughness,crystalline nature and stoichiometry of the a-IGZO samples.On the other hand,optical transmittance is apparently influenced by RF power where the extracted optical band-gap value increases from 3.48 to 3.56 eV with RF power varying from 40 to 80 W,as is supposed to result from the carrierinduced band-filling effect.The rise in RF power can also affect the performance of a-IGZO TFTs,in particular by increasing the field-effect mobility clearly,which is assumed to be due to the alteration of the extended states in a-IGZO thin films.

As_2S_8 planar waveguide:refractive index changes following an annealing and irradiation and annealing cycle,and light propagation features

The refractive index ofas-evaporatedamorphous semiconductor As2S8 film upon an annealing and saturation irradiation and annealing cycle is reversible. Upon successive treatment with annealing and non-saturation irradiation and further annealing, the refractive index of the as-evaporated amorphous semiconductor As2S8 film reaches a maximum value and then its reversibility occurs upon annealing. The annealing of the amorphous semiconductor AS2S8 films results in the stabilization of the structure through changes of the S-S bonds in the nearest environment, accompanied by a decrease of film thickness. The As2S8 planar waveguide after annealing （130 ℃） and saturation irradiation and annealing （130 ℃） shows a good propagation characteristic with ca, 0.27 dB/cm low propagation loss of the 632.8 nm guided mode.