Structural and electrical characterization of photodetectors based on III-V nitrides
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Date
2006-02
Authors
Lee, Yan Cheung
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Abstract
This project is a study about the structural and electrical characterization of
photodetectors based on III-V nitrides wide band gap semiconductors, namely gallium
nitride (GaN) and aluminium gallium nitride (AlxGal-xN). The initial investigation
includes the studies of metal-semiconductor-metal (MSM) photodetectors
(photodiodes) which are based on low growth temperature amorphous and
microcrystalline GaN grown on silicon (Si) substrates. Due to their smaller band gap,
these photodiodes will not be totally visible blind in terms of UV photodetection
applications. As a comparison, the microcrystalline GaN may promise a better
prospect in UV detector application due to its similarity to normal high temperature
grown GaN properties where the improvements that still need to be done could be the
crystalline quality, the device dimension, and the introduction of a buffer layer between
the Si and the GaN layer. The low dark current level of the amorphous GaN based
photodiode also indicate a large dark resistance, where this behaviour is often
desirable for photodetector application. However, a low reverse breakdown voltage at
4.3V of the amorphous photodiode is undesirable, thus preventing it from high power
application. In addition, the low mobility nature of the amorphous GaN based
photodetector will pose a threat to the speed of response, where the optimization that
can be done on the device is yet to be discovered. As for the high temperature grown
or normal single crystalline III-V nitrides based photodetectors, thermal annealing
treatment will enhance the electrical properties of the devices but it is also a critical
process to the stability of the contact structures. Here, the introduction of cryogenic
quenching treatment right after thermal annealing treatment has produced a better
device quality in terms of its electrical and structural properties when compared to the
annealing only treatment to the device. Overall, the improvement in the dark current
characteristics (dark current reduction) or the Schottky contact properties can be
achieved significantly through high temperature annealing treatment, i.e. at about 600-
700°C for nickel (Ni) Schottky based III-V nitrides MSM photodiodes. As for Ni AIGaN
Schottky diodes, the optimized temperature for the lowest leakage current (highest
Schottky barrier height) can be achieved at 40QoC. For all the studies, cryogenic
quenching treatment right after thermal annealing treatment is highly recommended to
yield better results. Further annealing treatment with cryogenic quenching treatment of
GaN MSM photodiodes have been studied briefly, and it has been found useful in
further reducing the dark current level of the devices.
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Keywords
The structural and electrical characterization of photodetectors , based on III-V nitrides wide band gap semiconductors