SiC and GaN are power semiconductor materials which have big band gap characteristics and capability to control high current.
|Chemical composition / condition||FTIR, Raman|
|Carrier Concentration of SiC Crystal||Raman|
Evaluation of Carrier Density
Collective oscillation of free electron which exists in n-type semiconductor as carrier is called as Plasmon, which is longitudinal wave similar to sound wave. This plasma oscillation is the same kind of wave as the longitudinal wave due to lattice vibration, LO phonon and therefore they interact with each other. It is known that the Raman peak due to such interaction shifts to higher wavenumber side with broadening peak shape when carrier concentration is increased and accordingly, the absolute carrier concentration is evaluated by the peak position. In this example, 3 kinds of 4H-SiC monocrystal were measured using JASCO NRS-5500 Raman Spectrophotometer. Raman spectroscopy makes it possible to evaluate sample in micron level spatial resolution which is difficult by the technique for Hall measurement, to analyze surface by imaging and also to evaluate depth profile with ease as non-destructive method.
Raman Spectra of Comparison about Carrier Density of 4H-SiC
NRS-5500 Laser Raman Spectrophotometer
Evaluation of SiC Crystal Polymorphism
It is well known that SiC has more than 200 different types of polymorphism depending on atomic arrangement and each polymorphism has different physical property. Among such many types of polymorphism, there are the most valuable ones starting from 4H polymorphism which has the biggest band gap and also high mobility and the trials have been attempted to grow crystals selectively as one of hot topics and challenge in field. Raman spectroscopy can evaluate and determine the type of polymorphism by analysis of peak patterns due to lattice vibration of crystals, appearing in low wavenumber region where the measurement is quite difficult by IR spectroscopy.
Raman Spectra of 6H-SiC and 4H-SiC