What are High-Performance Si APDs?

High-performance silicon avalanche photodiodes (Si APDs) provide gain, high sensitivity, and fast response for operation in demanding applications. Si APDs are available in various package styles and configurations, including back-illuminated, extended InGaAs wavelengths, and surface mount. The silicon substrate offers a low noise floor, making it suitable for applications that require low dark current and high signal-to-noise ratio (SNR).

The internal gain of these detectors is the result of the impact ionization process that occurs when photons are absorbed in the diode depletion region. The freed electrons then collide with other atoms within the diode material resulting in further electron generation. This process continues until a stable number of free electrons is reached for a given reverse bias voltage applied to the diode. This stabilization is called “gain saturation.”

How are High-Performance Si APDs Used?

High-performance silicon avalanche photodiodes (APD) are a key component in fiber optic receivers. These devices are used to detect light in systems that require high sensitivity and low noise. In our latest generation of receivers, the APD is based on a specially designed silicon substrate, which significantly improves the receiver’s sensitivity.

The new APD is a true substrate breakdown device, with a quenching resistor implemented on the same substrate as the detector. This brings several benefits to the receiver:

• Low dark current and high gain
• High sensitivity at all operating temperatures
• Large active area, which increases signal throughput and improves noise performance. There is also an added integrated temperature sensor, which allows the receiver to compensate for variations in temperature over time. This ensures stable and repeatable operation, regardless of ambient temperature fluctuations.

What are the Characteristics of High-Performance Si APDs?

High-performance Silicon Avalanche Photodiodes (Si APDs) have the following characteristics:

1. High quantum efficiency– A photodiode is designed to convert light energy into electric current. However, in the process of converting light energy into electric current, a certain amount of light energy is lost and appears as heat. The ratio of electricity generated to total light energy received is called quantum efficiency (QE). The high-performance Si APD has a high QE, which means that it can convert more light energy into electric current and thus have a higher output current or voltage.
2. High gain-The avalanche multiplication factor of the high performance Si APDs is determined by the reverse bias voltage and other design parameters. The higher the gain, the greater the output current or voltage for a given input optical power.
3. Large active area-The larger the active area, the stronger the optical power that can be received and converted into electricity to provide sufficient signal strength for practical applications.
4. Low dark current and low noise-When there is no incident light, there will be a small leakage current in the photodiode due to thermal effects, which is called dark current; and due to thermal impact, there will be some random fluctuation in the generated
5. High breakdown voltage– Breakdown voltage is the minimum amount of reverse bias that can permit a current to flow through a diode. For silicon avalanche photodiodes (Si APDs), it is usually about 60 V for semi-insulating substrate and about 30 V for an intrinsic substrate.

What are the Benefits of High-Performance Si APDs?

Unlike traditional Si APDs, High-Performance Si APDs use a patented design to create a high-gain and high-bandwidth avalanche multiplication region. This design makes it possible to operate the detector at higher bias voltages, resulting in stronger signal output.

The benefits of a stronger signal include:

• Better sensitivity, allowing you to detect lower intensity signals
• Better dynamic range, allowing you to detect signals over a wider range of intensities
• Higher bandwidth, allowing you to capture higher frequency signals
• Higher gain, allowing your system’s overall gain to be lowered (which can improve noise performance and help avoid saturation).

Bottom Line

The main benefit of using Si APDs over other types of photodiodes is their ability to detect low light levels at high speed. This is achieved through the use of an avalanche effect. This effect occurs when photons are absorbed by the depletion region of the device, creating electron-hole pairs. The strong electric field within the depletion region accelerates these charges and causes them to collide with other atoms, resulting in more electron-hole pairs being created. 

This multiplication process continues until the original charge carriers have reached the device’s junction, where they are collected as current flow. The multiplication process takes place at a very high speed, resulting in fast current responses from Si APDs. These devices can also detect light levels over a wide dynamic range, making them ideal for use in spectroscopy and optical sensing applications.