Hengjing Tang

Deep-level traps induced dark currents in extended wavelength InxGa1−xAs/InP photodetector

The dark current mechanism of extended wavelength InxGa1−xAs photo-detectors is still a debated issue. In this paper, the deep-level transient spectroscopy (DLTS) and dark current characteristics of InxGa1−xAs/InP detectors are investigated. Using trap parameters obtained from DLTS measurement, the device simulations of current-voltage characteristics are carried out by Silvaco Altas. The results reveal that the dark current at the low reverse bias voltage is associated with deep level trap induced trap assisted tunneling and Shockley-Read-Hall generation mechanism. The reduction of the deep level trap concentration in InxGa1−xAs absorption layer could dramatically suppress the dark current near zero bias in extended wavelength InxGa1−xAs/InP detectors.

2.6 μm MBE grown InGaAs detectors with dark current of SRH and TAT

We fabricate 2.6 μm InGaAs photodetectors by MBE technology and study its dark current mechanisms. Deep-level transient spectroscopy (DLTS) demonstrates a deep-level trap located at E c - 0.25 eV in the absorption layer. Using the trap parameters, a dark current model is constructed and the device simulation generates the dark current characteristic which agrees well with the experimental data. The model suggests that the dark current at low reverse voltage is dominated by the Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT). Furthermore, it predicts some basic rules for suppressing the dark current in 2.6 μm InGaAs detectors.

Effects of an anodic oxide passivation layer on mesa-type InGaAs (PIN) photodetectors

Because of the high density of surface states and large surface recombination velocity found in III–V materials, surface passivation remains a crucial processing step for the fabrication of mesa-type InGaAs photodetectors. It is required to find an easy and economical method to form an effective passivation layer on the surface of the detector. In this work, an oxide passivation layer formed by electrochemical anodization was proposed and a 256-element In0.78Ga0.22As photodetector array was fabricated. The dark current performance achieved is as low as 2 × 10−7 A (bias voltage of −0.1 V) at 300 K. The reduction of dark current indicates that the anodic oxide passivation layer is effective in reducing recombination at the exposed mesa surface.

Performance of extended wavelength InGaAs/InAsP SWIR detector

The single-pixel extended wavelength mesa InGaAs/InAsP SWIR detector was reported. The properties of the detector were characterized and analyzed at 160K~300K. At the operating temperature of 200K , the dark current density is 1.37×104 nA/cm2(@-10mV), the cut-off wavelength is 2.43μm, the peak detectivity and the peak responsivity are 3.44×1011cmHz1/2W-1 and 1.41A/W, respectively. Through analysis of the dark current source, the analysis of reverse dark current indicates that the tunneling current plays an important role at high voltage or relatively low temperature, and at near room temperature and low bias voltage, the generation-recombination current is the main current source instead of ohmic current based on thermal activation energy approximate to Eg/2 and the bias-voltage characteristic of the first order derivative of dark current, while the zero-voltage current mainly consists of the interface current and the thermal background current.

Study on dark current of extended wavelength InGaAs detectors

The short wavelength infrared (SWIR) band near 1.0-3.0μm plays an important role in many applications such as weather forecast, earth environmental or resource observation, low light level systems and astronomical observation. It is well known that InGaAs detectors can shift the cutoff wavelength from 1.7μm to 2.5μm with the higher fraction of indium in the ternary InXGa1-XAs material grown on InP, which results to material defects and poorer device characteristics due to the lattice mismatch. Dark current characteristics of extended wavelength InGaAs detectors were investigated in this paper. Dark current mechanisms for extended InGaAs detectors with different absorption layer parameters and device fabrication process were analyzed according to current-voltage curves at different temperatures and bias voltages. Activation energy of devices was extracted from current-voltage curves. Activation energy is related with absorption layer concentration and test temperature. Activation energy is the higher for the devices with the higher absorption layer concentration at lower bias voltage at the same temperature range, which shows that the narrower width of the depletion layer in the devices results to the lower generation-recombination current. The devices with the optimized etching and passivation parameters show higher thermal activation energy and the lower dark current. Dark current mechanisms of the ones are dominated by diffusion current at the higher temperature and lower bias voltage, whereas dominated by internal generation-recombination current and ohmic leakage current at the lower temperature.

Dark current simulation of InP/InGaAs/InP p-i-n photodiode

We report on 2D simulations of dark current for InP/InGaAs/InP p-i-n photodiode by Sentaurus DEVICE. Our simulation result is in good agreement with experiment indicating that generation-recombination is the dominant source of dark current at low bias. Effects of absorption layer thicknesses and doping concentrations on dark current are investigated in detail.

Impact of SiNx passivation on the surface properties of InGaAs photo-detectors

We investigate surface passivation effects of SiNx films deposited by inductive coupled plasma chemical vapor deposition (ICPCVD) and plasma enhanced chemical vapor deposition (PECVD) technologies for InAlAs/InGaAs/InP photo-detectors. It is found that ICPCVD deposited SiNx film effectively reduces the densities of the interface states and slow traps near SiNx/InAlAs interface, which realize the small surface recombination velocity and low surface current for InAlAs/InGaAs/InP photo-detectors. By comparing C-V and XPS results, it is suggested that the trap density reduction by ICPCVD technology could be attributed to the disorder suppression on InAlAs surface due to the high density of SiNx film and less processing energy to the InAlAs surface.

Anomalous capacitance in temperature and frequency characteristics of a TiW/p-InP Schottky barrier diode

The capacitance-voltage (C–V) and conductance voltage (G/ω–V) characteristics of a TiW/p-InP Schottky barrier diode (SBD) are measured at 310 K in the frequency range from 10 kHz to 1 MHz and the temperature dependency of the diode from 310 K to 400 K at 1 MHz are also investigated. Anomalous peaks and negative capacitances caused by interface states (N ss ) and series resistance (R s) are discussed, which strongly influence the electrical characteristics of SBD. R s is calculated from the measured capacitance (C m ) and conductance (G m ) values, indicating that the effects of R s are apparent at low frequency. The corrected capacitance (C c) and corrected conductance (G c) are both obtained from the C m and G m values by taking into account R s. The experimental results clearly show that the capacitance (C) and conductance (G) values are strongly dependent on the temperature and frequency.

Noise characteristics of short wavelength infrared InGaAs linear focal plane arrays

A noise characteristics model is presented for short wavelength infrared (SWIR) focal plane arrays (FPAs). The model shows the relationship between noise and varying integration time. The experimental results for different SWIR InGaAs linear FPAs in the 1.0–1.7 μm and 1.0–2.4 μm spectral range can be well fitted by this model. The noise of InGaAs FPAs with the conventional process in the 1.0–1.7 μm spectral range is determined by the shot noise from the photodiode, which provides a direction for reducing the noise of FPAs. The noise of InGaAs FPAs with the improved process in the 1.0–1.7 μm spectral range is determined by the noise from the readout integrated circuit (ROIC), which is due to the lower shot noise from the dark current of the photodiode. The noise of InGaAs FPAs in the 1.0–2.4 μm spectral range shows a transition from the fixed-pattern noise to the shot noise with a decrease of temperature as indicated by the model. This reduction is mainly due to the higher dark current of photodiodes and t...

Effect of sulfur passivation on the InP surface prior to plasma-enhanced chemical vapor deposition of SiNx

The fabrication of Au/SiNx/InP metal–insulator–semiconductor (MIS) diodes has been achieved by depositing a layer of SiNx on the (NH4)2Sx-treated n-InP. The SiNx layer was deposited at 200 °C using plasma-enhanced chemical vapor deposition (PECVD). The effect of passivation on the InP surface before and after annealing was evaluated by current–voltage (I–V) and capacitance–voltage (C–V) measurements, and Auger electron spectroscopy (AES) analysis was used to investigate the depth profiles of several atoms. The results indicate that the SiNx passivation layer exhibits good insulative characteristics. The annealing process causes distinct inter-diffusion in the SiNx/InP interface and contributes to the decrease of the fixed charge density and minimum interface state density, which are 1.96 × 1012 cm−2 and 7.41 × 1011 cm−2 eV−1, respectively. A 256 × 1 InP/InGaAs/InP heterojunction photodiode, fabricated with sulfidation and SiNx passivation layer, has good response uniformity.