Wenjuan Wang

Scanning capacitance microscopy investigation on InGaAs/InP avalanche photodiode structures: Light-induced polarity reversal

Cross-sectional scanning capacitance microscopy is applied to study the carrier distribution as well as its variation under irradiation in an InGaAs/InP avalanche photodiode. The photocarriers excited by the stray light of atomic force microscope laser beam lead to a dramatic deviation of the dC/dV profile in the unintended-doped absorption layer, and even cause the reversal of signal polarity. The existence of surface potential and its impact on the spreading of photocarriers near the cleaved face are demonstrated as the main origins of the light-induced dC/dV reversal. The effect provides experimental information on the distribution property of photoelectric process in devices.Cross-sectional scanning capacitance microscopy is applied to study the carrier distribution as well as its variation under irradiation in an InGaAs/InP avalanche photodiode. The photocarriers excited by the stray light of atomic force microscope laser beam lead to a dramatic deviation of the dC/dV profile in the unintended-doped absorption layer, and even cause the reversal of signal polarity. The existence of surface potential and its impact on the spreading of photocarriers near the cleaved face are demonstrated as the main origins of the light-induced dC/dV reversal. The effect provides experimental information on the distribution property of photoelectric process in devices.

Tunable Photodetector Based on GaAs/InP Wafer Bonding

We demonstrate a tunable long wavelength vertical-cavity photodetector which is fabricated by bonding a GaAs-based tunable filter with an InP-based absorption structure. The wavelength tuning range of 10.5 nm was achieved via thermal-optic effect. The external quantum efficiency of about 22%, the spectral linewidth as narrow as 0.6 nm, and the 3-dB bandwidth of 12 GHz were obtained in the device

Numerical analysis of single photon avalanche photodiodes with improved structure

In this paper, the effects of the thickness of the multiplication region (Tm), the sheet charge density of the charge control layer (Dc) and the guard ring design to a separate absorption, grading, charge, and multiplication InGaAs/InP single photon avalanche diode (SPAD)s performance are numerically discussed. Optimized Tm and Dc are designed for a SPAD. Implanted guard ring is revealed to be easier and better to suppress the junction edge electric field compared with the floating guard ring.

Nonequilibrium carrier distribution in semiconductor photodetectors: Surface leakage channel under illumination

The nonequilibrium carrier distribution in an InGaAs/InP avalanche photodiode under light illumination is obtained by cross-sectional scanning capacitance microscopy combined with numerical simulation. The sheet density of negative surface charge is determined to be 1.85×1010u2002cm−2 on the native-oxidized InGaAs (110) face. This surface charge is found responsible for the accumulation of minority holes, which leads to an inversion layer at the sidewall surface of device in the absorption region under illumination exceeding 0.1u2002mW/cm2. The inversion depth increases up to 200 nm along with the enhancement of excitation intensity. This work suggests that a surface leakage channel may form in semiconductor photodetectors through detection light excitation.

Effect of surface charge on the dark current of InGaAs/InP avalanche photodiodes

The effects of surface charge on the dark current of the separate-absorption-grading-charge-multiplication InGaAs/InP avalanche photodiodes (APDs) are discussed using drift-diffusion simulation. The dark current increases exponentially with the increasing of surface charge density, and gets multiplied, thus influencing the performance of the APDs, especially in Geiger mode. The mechanism of the surface charge leakage current is discussed, and a floating guard ring structure is proposed to suppress the influence of surface charge effectively.

InGaAs/InP single photon avalanche diodes with low tunneling current

Avalanche photodiodes(APDs) have attracted more and more attention due to their single photon detection ability. However, low dark current is a prerequisite for APDs which are used as single photon avalanche photodiodes (SPADs).In this work,Planar-type Separate Absorption Grading Charge Multiplication(SAGCM) InP/InGaAs APD are fabricated and simulated with ISE-TCAD. We present a detailed analysis of dark current and gain experimentally and theoretically. The effect of the generation-recombination process,the tunneling process,the surface leakage process and the multiplication process on the total dark current are discussed.The dark current gain ratio (Id/M) is used to demonstrate the tunneling current. Simulation results indicate that the thickness of multiplication and trap-assisted tunneling effect have a great influence on the tunneling current:thin multiplication layer and traps will lead to a substantial increase in the tunneling current component, therefore appropriate multiplication layer thickness and low traps are necessary to obtain good APDs with low dark current. Compared with the simulation results,it shows that our APDs have low tunneling current even at breakdown point.In addition, the distinctions between different process of dark current provide a good guidance for the optimization of the APD.

Room-temperature single-photon detector based on single nanowire

Single-photon detectors that can resolve photon number play a key role in advanced quantum information technologies. Despite significant progress in improving conventional photon-counting detectors and developing novel device concepts, single-photon detectors that are capable of distinguishing incident photon number at room temperature are still very limited. We demonstrate a room-temperature photon-number-resolving detector by integrating a field-effect transistor configuration with core/shell-like nanowires. The shell serves as a photosensitive gate, shielding negative back-gated voltage, and leads to a persistent photocurrent. At room temperature, our detector is demonstrated to identify 1, 2, and 3 photon-number states with a confidence of >82%. The detection efficiency is determined to be 23%, and the dark count rate is 1.87 × 10-3 Hz. Importantly, benefiting from the anisotropic nature of 1D nanowires, the detector shows an intrinsic photon-polarization selection, which distinguishes itself from existing intensity single-photon detectors. The unique performance for the single-photon detectors based on single nanowire demonstrates the great potential for future single-photon detection applications.

Origin of large dark current increase in InGaAs/InP avalanche photodiode

The large dark current increase near the breakdown voltage of an InGaAs/InP avalanche photodiode is observed and analyzed from the aspect of bulk defects in the device materials. The trap level information is extracted from the temperature-dependent electrical characteristics of the device and the low temperature photoluminescence spectrum of the materials. Simulation results with the extracted trap level taken into consideration show that the trap is in the InP multiplication layer and the trap assisted tunneling current induced by the trap is the main cause of the large dark current increase with the bias from the punch-through voltage to 95% breakdown voltage.

Plasmonic optical convergence microcavity based on the metal-insulator-metal microstructure

With the increasing demand of low noise detection, the dimension of detectors are becoming smaller and smaller to reduce the dark current while sacrificing the detection efficiency. Here, a metal-insulator-metal (MIM) optical microcavity is proposed to converge light from tens of micrometers to several micrometers with little divergence. The measured transmission peaks show obvious dependence on the top metallic grating parameters, indicating the surface plasmon polariton resonance inside the cavity. Scanning near-field optical microscopy reveals the output profile around the exit holes. Polarization selective transmission has been demonstrated. If combined with a photodetector, the MIM microcavity, due to its light convergence capability, would provide a possibility to reduce the detectors active dimension down to 1–2u2009μm while retaining high quantum efficiency by keeping a large light collection area.

High differential gain single photon avalanche photodiode with improved structure

An InGaAs/InP single-photon avalanche photodiode (SPAD) with a high differential gain was achieved by changing the multiplication region thickness and the sheet charge density of the charge layer. A gain of more than 100 was obtained. The DCR is less than 1k with the frequency up to 250 kHz.