當操作在線性模式(0.95Vbr)，主動區直徑60μm的元件擁有19.6A/W的高響應度及 >5.6mA的1-dB飽和電流。使用主動區直徑為200μm的元件能同時擁有14.6mA的高飽和電流及1.4GHz的光電頻率響應。這種新穎式結構相比於之前雙層累增層的元件和高性能的商用元件，只需較低的本地震盪器輸出功率(0.5 vs. 4mW)，便能在我們實驗室自己建立的FMCW光達系統中表現出高訊雜比及高品質的3D成像。
;To date APDs have come to play an important role at the receiving end in several different applications, such as light detection and ranging(LiDAR), photon number resolving(PNR), quantum key distribution(QKD) and quantum computing. In this work, a novel avalanche photodiode (APD) design is demonstrated which overcomes the fundamental trade-off between responsivity and saturation current performance found in the traditional APDs, for receiver-end applications in single photon detection and frequency modulated continuous wave (FMCW) LiDAR.
In this novel vertically-illuminated APD, which can deliver remarkable performances in both the linear and Geiger mode operations. The adoption of multiple (triple) In0.52Al0.48As based M-layer makes the avalanche process become more pronounced under a much less effective critical field compared to the dual M-layer reference device. The decrease of the E-field required in our active M-layer ensures that a stronger E-field can be allocated to the thick absorption layer with a smaller breakdown voltage for APD operations. This in turn leads to a less serious space-charge screening effect and less device heating under a high output photocurrent. By combining the etch mesa type with this cascaded M-layer structure, the electric (E-) field at the sidewall of the M-layer can be suppressed to 2kV/cm.
Under linear mode (0.95Vbr) operation, it can achieve high responsivity(19.6A/W), high 1-dB saturation current(>5.6mA), using the demonstrated APD with its 60 µm diameter active window. Extremely high saturation current (>14.6mA), and decent O-E response (1.4 GHz) can be simultaneously achieved using the demonstrated APD with its 200 µm diameter active window. This novel APD exhibits a larger signal-to-noise ratio in each pixel and much better quality of constructed 3-D images in home-made FMCW LiDAR system than those of obtained with the reference dual M-layer sample and high-performance commercial p-i-n PD modules, with much less optical local-oscillator(LO) power required (0.5 vs. 4mW).
Under Geiger mode, the single-photon detector(SPD) cooled to 225 K for high single-photon detection efficiency(SPDE) of 74%, lower dark count rate (DCR), and neat temporal characteristic of 101ps without the involvement of afterpulsing at short hold-off time(50ns). These results strongly support that such novel single-photon detector can further enhance the sensitivity of the next generation ToF LiDAR system.
