雪崩光电二极管(APD)(又称累崩光电二极管或崩溃光二极体)是一种半导体光检测器，其原理类似于光电倍增管。在加上一个较高的反向偏置电压后（在硅材料中一般为100-200 V），利用电离碰撞（雪崩击穿）效应，可在APD中获得一个大约100的内部电流增益。某些硅APD采用了不同于传统APD的掺杂等技术，允许加上更高的电压(>1500 V)而不致击穿，从而可获得更大的增益(>1000)。一般来说，反向电压越高，增益就越大。APD倍增因子M的计算公式很多，一个常用的公式为

其中L是电子的空间电荷区的长度，而是电子和空穴的倍增系数，该系数取决于场强、温度、掺杂浓度等因素。由于APD的增益与反向偏置和温度的关系很大，因此有必要对反向偏置电压进行控制，以保持增益的稳定。雪崩光电二极管的灵敏度高于其它半导体光电二极管。

An avalanche photodiode (APD) is a highly sensitive semiconductor electronic device that exploits the photoelectric effect to convert light to electricity. APDs can be thought of as photodetectors that provide a built-in first stage of gain through avalanche multiplication. From a functional standpoint, they can be regarded as the semiconductor analog to photomultipliers. By applying a high reverse bias voltage (typically 100-200 V in silicon), APDs show an internal current gain effect (around 100) due to impact ionization (avalanche effect). However, some silicon APDs employ alternative doping and beveling techniques compared to traditional APDs that allow greater voltage to be applied (> 1500 V) before breakdown is reached and hence a greater operating gain (> 1000). In general, the higher the reverse voltage the higher the gain. Among the various expressions for the APD multiplication factor (M), an instructive expression is given by the formula