AlInAsSb Staircase Avalanche Photodiode

Physical Sciences : Electrical

Available for non-exclusive licensing


  • Seth Bank, Ph.D. , Electrical and Computer Engineering
  • Scott Maddox, Ph.D. , Microelectronics Research Center
  • Min Ren , University of Virginia
  • Wenlu Sun , University of Virginia
  • Madison Woodson , University of Virginia
  • Joe Campbell , University of Virginia
  • Yaojia Chen , University of Virginia

Background/unmet need

An avalanche photodiode (APD) is a highly sensitive semiconductor electronic device that exploits the photoelectric effect to convert light to electricity. The internal gain of APDs can provide higher sensitivity than p-i-n photodiodes, which is beneficial for many optical communication, spectroscopy, and sensing applications.

However, the origin of the APD gain is impact ionization, a stochastic process that results in excess noise and limits the gain-bandwidth. For the past four decades, reducing the excess noise factor has been a focus of APD research and development. One structure that can achieve very low noise is the staircase APD.

Unlike conventional APDs, in which impact ionization occurs relatively uniformly throughout the entire multiplication region, in the staircase structure, avalanche events occur proximate to the sharp bandgap discontinuity. These discontinuities function somewhat like dynodes in a photomultiplier in which the gain position is localized. As a result, the gain process is more deterministic, with concomitant reduction in gain fluctuations and, thus, lower excess noise.

Unfortunately, initial studies of staircase APDs used the AlxGa1-xAs material system, which has inadequate band offsets. As a result, the projected noise characteristics were never achieved.

Invention Description

A group led by Prof. Seth Banks at The University of Texas at Austin and Prof. Joe Campbell at the University of Virginia explored a staircase APD with a staircase multiplication region composed of a graded AlInAsSb alloy, lattice matched (or psuedomorphically strained) to either InAs or GaSb. The group has discovered that this alloy is a particularly good fit for this purpose, as it exhibits:

- a direct bandgap over a wide range of compositions
- large conduction band offsets much larger than the smallest achievable bandgap
- small valance band offsets

This is the first staircase alloy to exhibit all three of these critically important characteristics. 


  • Extremely low noise-to-signal ratio and high gain APD, capable of detection of extremely weak light
  • Linear-mode photon counting at bandwidths in excess of 1 GHz
  • Operating wavelengths ranging from visible to far-infrared (teraHertz) can be achieved by varying the bandgap of a separate absorption region
  • Can be operated at room temperature
  • Photon counting bandwidth is over 100 times higher than Geiger mode APDs

Market potential/applications

The invention can be used to create extremely low-noise, high-gain avalanche photodiodes operating at wavelengths ranging from the visible all the way out to the far-infrared, by varying the bandgap of a separate absorption region. With an appropriate design, such a device, operating at room temperature, may provide high-speed, linear-mode, single-photon counting at the fiber-optic telecommunications wavelengths of 1.3 and 1.55 um, thereby revolutionizing the field quantum telecommunications, which currently lacks such a detector.

The same device could also be used to improve the range of traditional fiber-optic telecommunications. The invention may also benefit applications requiring sensitive detectors at other wavelengths such as fluorescence spectroscopy, LIDAR (laser ranging), remote-gas sensing, and thermal imaging. 

Development Stage

Lab/bench prototype

IP Status