Novel InGaAs/InAlAs travelling wave avalanche photodiode for ultra high speed photonic applications

Lead Research Organisation: University of Sheffield
Department Name: Electronic and Electrical Engineering


The explosive use of internet has increased the demand for high speed photodetectors to convert optical signal to electrical signal at 2.5Gb/s, 10Gb/s or 40Gb/s optical communication systems. High sensitivity photodetectors that can detect very low light level are important to improve the signal quality and increase the transmission distance and hence lower the cost of these systems. They are also required in sequencing of the human genome, in medical imaging and in future quantum computing. Semiconductor avalanche photodiodes (APDs) can offer the high sensitivity required for these applications and are robust, cheap, compact and efficient. In APDs an electron-hole pair can trigger an avalanche of electrons and holes (like the snow avalanche effect). This multiplication process provides an internal gain which improves the sensitivity of APDs. In most semiconductors, there is significant statistical fluctuation in the multiplication process giving rise to unwanted excess noise. Low excess noise is important and this can be achieved by using a material in which electrons can multiply much easier than holes (or vice versa).In optical communication systems infrared light with a wavelength of 1550nm is used to transmit information to minimise loss in the optical fiber. Because of this we will have to use APDs fabricated using a semiconductor called InGaAs as an absorption layer to detect infrared light of 1550nm and another semiconductor, InAlAs, as the multiplication layer to produce the avalanche effect. InAlAs produces less excess noise compared to currently available commercial APDs at 1550nm because electrons can multiply much easier than holes in this material. From our research we know that we can further reduce the excess noise by using very thin sub-micron multiplication layer (< 1/50 of the diameter of our hair) and carefully engineer the electric field profile in the InAlAs multiplication layer. We have shown that these techniques can reduce the excess noise leading to higher sensitivity APD. In this project we will grow, fabricate and characterise a number of different designs to minimise the excess noise in our APDs. Another important parameter of APDs is the bandwidth since they operate at very high data rate up to 40Gb/s. To achieve high bandwidth we will incorporate the following innovations; Firstly, we will use very thin sub-micron absorption and multiplication layers to reduce the electron and hole transit times. To ensure that the infrared light is absorbed efficiently we will confine the light in a special structure called optical waveguide. By integrating the APD with a waveguide the infrared light will be efficiently absorbed to yield high speed high sensitivity waveguide-APD. Secondly, we are going to design the waveguide-APD into a structure called travelling wave-APD which has characteristics of an electrical transmission line. This structure will ensure that high speed signals are transmitted efficiently from our APD to the external circuit. We will use a theoretical model to predict the characteristics of the travelling-wave to make sure that they can produce high sensitivity at frequency up to 40GHz.There are several experiments that we will perform to give us the understanding we need to produce a high speed high sensitivity photodetector. Measurements on the APDs to monitor how the multiplication changes with temperature ranging from room temperature down to -250 degree Celcius as well as how the multiplication changes when the signal frequency is increased up to 40GHz will be carried out. This will provide us the data and understanding required to produce very high sensitivity photodetectors for optical communication systems as well as many other applications such as for medical imaging, environmental pollutant monitoring, defects monitoring in manufacturing and many other areas that affect our daily lives.
Description Developed an optical detectors suitable for optical fibre communication and range measurement using optical time of flight technique. The detectors can provide high amplification to achieve high detection efficiency.
Based on this technology, we have developed single photon detectors.
Exploitation Route The work has led to two projects funded by a company to design detectors for an optical system to measure distance.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Environment,Manufacturing, including Industrial Biotechology

Description Two knowledge transfer project fully funded by a company (LaserTel) have been secured. Some of the work has also contributed to a successful and ongoing TSB KTP project with LAND Instruments International. The expertise accumulated is being exploited to manufacture sensors in LAND's product. Currently there is an ongoing discussion with Huawei to explore a new project based on this technology.
Sector Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software)
Impact Types Economic

Description InGaAs/InAlAs APDs for LIDAR systems
Amount £18,293 (GBP)
Organisation Lasertel Inc 
Sector Private
Country United States
Start 10/2012 
End 03/2013
Description InGaAs/InAlAs APDs for LIDAR systems Phase 2
Amount £24,114 (GBP)
Organisation Lasertel Inc 
Sector Private
Country United States
Start 05/2014 
End 09/2014
Description Next generation avalanche photodiodes: realising new potentials using nm wide avalanche regions
Amount £620,511 (GBP)
Funding ID EP/K001469/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 04/2013 
End 10/2016
Description Bookham Technology Plc 
Organisation Oclaro
Country United States 
Sector Private 
Start Year 2006
Description University of Texas at Austin 
Organisation University of Texas at Austin
Country United States 
Sector Academic/University 
Start Year 2006