| 摘要: | 單光子感測在光達、量子電腦與量子密鑰傳輸等應用中是相當重要的技
術。本文是以砷化銦鎵為基礎的單光子崩潰二極體進行研究，此元件可應用
於近紅外光纖通訊波段，又因其體積小、堅固、節能且不需致冷降溫，有利
於普及量子資訊科學應用。在光量子通訊與計算中的後端感測器除了須具
備單光子偵測能力，若能有光子數目解析的能力將大幅提升量子通訊的安
全性以及加速量子計算的開發。
單光子崩潰二極體是以脈衝閘壓蓋格模式下操作，以降低缺陷所導致的
後脈衝效應，脈衝的上升與下降邊緣會透過元件接面電容耦合至輸出，與真
實的崩潰訊號疊合，甚至埋沒崩潰訊號，因此需要增加超額偏壓以利辨識出
崩潰訊號，在高超額偏壓下，元件存在大量崩潰載子使得後脈衝效應變得嚴
重，因此在高速應用中常使用自差分電路消除電容耦合雜訊，以辨識微弱崩
潰訊號；又若要使元件具備光子數目解析能力，須讓元件在發生增益飽和之
前就截止，才能讓崩潰載子數量隨入射光子數目變化，因此最直接的作法為
降低閘壓脈衝寬度，此作法可同時降低後脈衝效應以及暗計數率，然而亦會
降低光偵測效率。
因此，本文設計一脈衝寬度調節器，將脈衝訊號分別輸入比較器和由電
阻產生延遲後的比較器的兩端再由及閘將同時輸出為正的訊號輸出，即可
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以將原本的脈衝寬度縮減到有效寬度在超額偏壓 3 %溫度為 250 K 時將近
1.1 ns，在短脈衝操作下所產生的微弱崩潰訊號則經由自差分電路可獲得良
好訊雜比。
在短脈衝寬度以及自差分電路的量測下，我們進行砷化銦鎵/砷化銦鋁
單光子崩潰二極體完整特性量測與探討，在有效脈衝寬度 1.1 ns、250 K、
9.9 MHz 的情況下，暗計數率僅 2 % ，與過往實驗室數據相比有大幅度的
降低，同時單光子偵測效率為 52 %，在如此的數據表現下對於光子數目解
析而言具有更大的優勢。
;Single photon detection is crucial to many applications, such as lidar, quantum
key distribution, and quantum computing. This thesis focuses on the study of
InGaAs based single photon avalanche photodiodes (SPAD) which can perform
single photon detection in the near infrared including fiber communication bands.
Due to their advantages of compact, robustness, efficient power consumption and
noncryogenic, the development of SPADs is instrumental for the widespread
application of quantum information science. In photonic quantum communication
and computing, the detectors having both the single photon sensitivity and photon
number resolving capability can definitely make a more secure quantum
communication and facilitate the development of quantum computer.
SPAD is usually operated under the gated Geiger mode for suppressing the
afterpulsing effect caused by defects. Under gated mode operation, the fast rising
and falling edge of pulse will be coupled through the junction capacitance of
SPAD to the output, generating a spikelike capacitive response superimposed with
avalanche signal and may bury weak avalanche pulses. Therefore, it is necessary
to increase the excess bias for discriminating the avalanche signal. Under such
high excess bias, there will be lots of avalanche carriers that induce serious
afterpulsing effect. Hence for high-speed applications, self-differencing circuit is
often used to suppress the spike noise for discriminating weak avalanche signal.
Moreover, for gifting SPAD with photon number resolving capability, the
avalanche process should be regulated such that the avalanche carriers become
proportional to the incident photon number. The most intuitive way to regulate the
avalanche process is to reduce the pulse width, which simultaneously eliminate
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the afterpulsing effect and reduce the dark count rate. However, it also degrades
the single photon detection efficiency.
In order to get the shorter pulse, we design a pulse width modulator. This
modulator input normal pulse signal into comparator and another comparator
which is delayed by a resistor. Then the “and” gate will output the signal when
the two signal from comparator are positive in the same time. Thus we can
generate a pulse signal with effective pulse width of nearly 1.1 ns at the excess
bias of 3 % and at 250 K.
Coordinating the short pulse operation with a self-different circuit, a very weak
avalanche signal can be successfully discriminated with good signal-to-noise ratio.
We further demonstrate a comprehensive study on the performance of
InGaAs/InAlAs SPAD. Under the condition of pulse width of 1.1 ns, excess bias
of 3 % and at 250 K, the dark count rate (DCR) of 2 % and the single photon
detection efficiency of 52 % are obtained, where the DCR is significantly
improved as compared to past work of our lab. With superior DCR performance
and short pulse operation, we anticipate to perform the photon number resolving
with our homemade SPAD. |
