Feature: Semiconductors Figure 1: Carbon impurities in GaN semiconductors affect device performance
Making Gallium Nitride a star semiconductor
By Professor Masashi Kato, Gallium Nitride semiconductor study lead, Nagoya Institute of Technology, Japan
T
he semiconductor industry and almost all of today’s electronics have been dominated by silicon for decades. But this may change,
as gallium nitride (GaN) emerges as a powerful – even superior – alternative. GaN semiconductors are considered a future alternative to silicon, not least due to their superior performance in fast switching applications.
GaN performance GaN semiconductors have been commercially available since the 1990s, often found in power devices due to their relatively larger bandgap than silicon’s, which makes them a better candidate for high-voltage and high-temperature applications. Moreover, current travels more quickly through GaN, which ensures fewer switching losses. Still, not everything about GaN is
ideal. While impurities are usually desirable in semiconductors, in GaN crystals they can degrade switching performance. Impurities such as carbon atoms often lead to poorer switching performance due to the trapping of charge carriers in the “deep” energy levels of the semiconductor material; see Figure 1.
30 June 2021
www.electronicsworld.co.uk Scientists from Nagoya Institute of
Technology in Japan have explored the mechanism behind the impact of carbon impurities on the charge carriers of GaN, paving the way for impurity control strategies in GaN crystal growth. An interesting experimental
manifestation of deep levels is the appearance of a long-lived yellow luminescence in the photoluminescence spectrum of GaN, along with a long charge carrier recombination time reported by characterisation techniques like time-resolved photoluminescence
(TR-PL) and microwave photoconduc- tivity decay (µ-PCD). However, the mechanism underlying this longevity is unclear. Scientists explored the effect of deep levels on yellow luminescence decay time and carrier recombination by observing how the TR-PL and µ-PCD signals changed with temperature. Only after understanding the
impact of impurities in GaN power semiconductor devices, can scientists push for the development of impurity control technologies in GaN crystal growth.
Figure 2: Semiconductor behaviour
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