The Need

Avalanche photodiodes (APDs) that target a wavelength of 1550 nm have several applications ranging from optical communications to imaging to single photon detection. There is increasing interest in APDs for longer wavelengths. A distinctive feature of an APD is high sensitivity due to the gain achieved by the impact ionization of carriers. However, this process also introduces excess noise that limits the signal to noise ratio of an APD. Therefore, there is a need for a novel photodetector design that can achieve high gain with low excess noise at long wavelengths.

The Technology

Ohio State University researcher Dr. Sanjay Krishna has developed a novel lateral interband Type II engineered (LITE) detector. A LITE is type of photodetector that uses engineered heterostructures to spatially separate electrons and holes into separate layers. The device may have two configurations, a positive intrinsic (PIN) configuration and a bipolar junction transistor (BJT) configuration. The PIN configuration may have a wide bandgap (WBG) layer that transports the holes above or below a narrow bandgap (NBG) absorber layer that absorbs the target radiation and transports the electrons. The BJT configuration may have a WBG layer operating as a BJT above or below an NBG layer. In both configurations, the LITE design uses a Type II staggered offset between the NBG layers and the WBG layers that provides a built-in field for the holes to drift from an absorber region to a transporter region. In addition to the built-in field caused by the heterojunction line up and doping profile, there is an additional applied field typically in the lateral direction.

Commercial Applications

• Optical communications: LITE detectors can be used for high-speed and long-distance optical communication systems that operate at long wavelengths, such as 1550 nm or beyond.
• Imaging: LITE detectors can be used for high-resolution and low-noise imaging applications, such as infrared cameras, night vision devices, or biomedical imaging.
• Single photon detection: LITE detectors can be used for quantum information processing and cryptography applications that require single photon detection at long wavelengths with high efficiency and low dark counts.

Benefits/Advantages

• High gain: LITE detectors can achieve high gain by exploiting both photoconductive gain and impact ionization gain in different layers of the device.
• Low excess noise: LITE detectors can achieve low excess noise by minimizing the impact ionization of holes in the WBG layer, which reduces the k-value.
• Long wavelength operation: LITE detectors can operate at long wavelengths by using NBG materials that have high absorption coefficients at these wavelengths, such as InAs or InGaAs.
• Lateral design: LITE detectors have a lateral design that allows for easy integration with other electronic components on the same chip, such as transistors, amplifiers, or readout circuits.