Structurally modified quantum dot infrared photodetector demonstrate high performance
Infrared (IR) cameras find a wide range of applications from military operations to medical diagnosis. A typical IR detector consists of photo detector arrays for detection of infrared waves, digital convertors to obtain thermal images, and finally, a cooling system like liquid nitrogen dewars. Quantum dot infrared photodetectors (QDIPs) can replace these systems because they would reduce the cost, size and weight of an IR camera. Prof. Chakrabarti’s group at IITBNF has made novel changes in the InAs/ GaAs quantum dot heterostructure, improving its performance as a QDIP.
QDIPs can operate at higher temperatures due to lower dark current (i.e. noise), and hence need only lighter cooling systems (e.g. thermoelectric coolers). Typically, QDIPs are layered structures of quantum dots made using III-V materials. The team proposes a new heterostructure – an extension of the standard InAs/ GaAs QDIPs, with additional stacks of ultra-thin capping (InAlGaAs) and barrier (GaAs) layers. They observed that quantum dots (QDs) increase in size progressively from the bottom to the top layers. This is due to strain between each QD layer and GaAs barrier layer. Fortunately, having such different sized QDs increases the absorption spectrum and area of the entire QDIP structure, therefore improving its efficiency.
The performance of these devices depends upon the thickness of the GaAs barrier layer – too thin a layer will allow current to tunnel through and add to the noise, whereas a thicker layer will release the strain coupling and lower efficiency by giving smaller dots. Prof. Chakrabarti’s team successfully demonstrated high performing, thermally stable QDIPs with an optimized GaAs barrier layer thickness. Compared to the standard InAs/ GaAs QDIP, it shows 10X increase in detectivity i.e. the signal to noise ratio.
- Shruti Karande
Work funded/ supported by: Dept. of Science & Technology (DST) of Government of India (GoI); IIT Bombay Nanofabrication Facility (IITBNF).
Published paper: Hemant Ghadi, Akshay Agarwal, Sourav Adhikary, Binita Tongbram, Arjun Mandal, Subhananda Chakrabarti, Naresh Babu Pendyala, Sachin Prajapati, and Ashwani Kumar, "Effect of barrier thickness on structural, optical, and spectral behaviors of vertically strain coupled InAs/GaAs quantum dot infrared photodetectors." Journal of Vacuum Science & Technology B 32.5 (2014): 051208.