Xiangyi Guo

Microstructured silicon photodetector

Photodetectors fabricated on microstructured silicon are reported. The photodetectors exhibited high photoresponse; at 3V bias, the responsivities were 92A∕W at 850nm and 119A∕W at 960nm. At wavelengths longer than 1.1μm, the photodetectors still showed strong photoresponse. A generation-recombination gain mechanism has been proposed to explain the photoresponse of these photodiodes. From measurements of the noise current density, the calculated gain was approximately 1200 at 3V bias.

Recent advances in avalanche photodiodes

Until the early 2000s, the avalanche photodiode (APD) was widely deployed in high-performance optical receivers that operated up to 10 Gb/s. In subsequent years, the use of APDs for high-capacity systems declined as a result of their limited gain bandwidth, the transition to coherent detection, and the development of high-efficiency modulation techniques. Recently, the rapid growth of optical-fiber communications systems that utilize baud rates up to 25 Gb/s represented by a 100-Gb/s Ethernet has led to a resurgence of research on APDs and the development of low-noise APDs with enhanced gain bandwidth. This paper presents a brief review of APD fundamentals and describes some of the recent advances.

Demonstration of ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes

We report ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes. An external quantum efficiency of 83% (187 mA/W) at 278 nm, corresponding to unity gain after reach-through was achieved. A gain higher than 1000 was demonstrated without edge breakdown.

High Detection Sensitivity of Ultraviolet 4H-SiC Avalanche Photodiodes

We report 4H-SiC p-i-n avalanche photodiodes (APDs) with very low dark current. When biased for a photocurrent gain M of 1000, a 100-mum-diameter device exhibits dark current of 5 pA (63 nA/cm2), corresponding to primary multiplied dark current of 5 fA (63 pA/cm2). The peak responsivity at unity gain is 93 mA/W (external quantum efficiency = 41%) at lambda = 280 nm. The excess noise factor corresponds to k = 0.1. Detection of several tens of femtowatts of ultraviolet light is reported.

High-Performance InGaAs/InP Single-Photon Avalanche Photodiode

In0.53Ga0.47As/InP avalanche photodiodes with very low dark current have been characterized in gated mode for single-photon detection. A 40-mum-diameter single-photon avalanche diodes (SPAD) exhibited high single-photon detection efficiency (SPDE = 45% at 1.31 mum), low dark count rate (DCR = 12 kHz), and low noise-equivalent power (NEP=4.5X 10-17W/Hz1/2 W/Hz) at 200 K and 1.31 mum. A timing resolution of 140 ps was achieved with an SPDE of 45%. In addition, the dark current and DCR of a 4X4 SPAD array are reported.

Study of reverse dark current in 4H-SiC avalanche photodiodes

Temperature-dependent current-voltage (I-V) measurements have been used to determine the reverse dark current mechanisms in 4H-SiC avalanche photodiodes (APDs). A pn junction vertical mesa structure, passivated with SiO/sub 2/ grown by plasma enhanced chemical vapor deposition, exhibits predominate leakage current along the mesa sidewall. Similar APDs, passivated by thermal oxide, exhibit lower dark current before breakdown; however, when the temperature is higher than 146/spl deg/C, an anomalous dark current, which increases rapidly with temperature, is observed. This current component appears to be eliminated by the removal of the thermal oxide. Near breakdown, tunneling is the dominant dark current mechanism for these pn devices. APDs fabricated from a pp/sup -/n structure show reduced tunneling current. At room temperature, the dark current at 95% of breakdown voltage is 140 fA (1.8 nA/cm/sup 2/) for a 100-/spl mu/m diameter APD. At a gain of 1000, the dark current is 35 pA (0.44 /spl mu/A/cm/sup 2/).

Low Dark Count Rate and High Single-Photon Detection Efficiency Avalanche Photodiode in Geiger-Mode Operation

An In0.53Ga0.47As-InP avalanche photodiode with very low dark current (0.15 pA at 95% breakdown voltage, 200 K) has been characterized in gated mode for single-photon detection. The temperature dependence of dark current and dark count yields activation energy of ~0.4 eV from 240 K to 297 K. High single-photon detection efficiency (SPDE) at telecom wavelengths with very low dark count rate (DCR) (e.g., DCR =12 kHz at SPDE =45% at 1.31 mum and 200 K) was achieved

21-GHz-Bandwidth Germanium-on-Silicon Photodiode Using Thin SiGe Buffer Layers

Backside-illuminated germanium photodiodes fabricated on silicon substrate with two Si xGe1-x buffer layers are reported. At 1.3 mum, the responsivity was 0.62 A/W for reverse bias greater than 0.1 V. The 3-dB bandwidth was 21.5 GHz at 10-V reverse bias, achieving a bandwidth-efficiency product of 12.6 GHz

Performance of Low-Dark-Current 4H-SiC Avalanche Photodiodes With Thin Multiplication Layer

The authors report on the fabrication and performance of low-dark-current 4H-SiC avalanche photodiodes with a thin 180-nm-thick p - multiplication layer. At a photocurrent gain M of 1000, the dark current of a 100-mum-diameter device was 35 pA (0.44 muA/cm2). The peak unity-gain responsivity was 100 mA/W (external quantum efficiency=46%) at lambda=268 nm, and at high gain, a responsivity greater than 107 A/W was achieved. The excess noise factor corresponds to k=0.12. Time-domain pulse measurements indicate an RC-limited unity-gain bandwidth of 300 MHz

Edge breakdown in 4H-SiC avalanche photodiodes

We report suppression of edge breakdown in mesa-structure SiC avalanche photodiodes (APDs) by employing a 10/spl deg/ sidewall bevel. These devices exhibit low dark currents, <10 pA for a 160-/spl mu/m-diameter device, at the onset of avalanche gain. Two-dimensional raster scans of both beveled and nonbeveled devices, fabricated from the same wafer, show the photocurrent as a function of position and illustrate the spatial properties of avalanche gain in SiC APDs.