Despite the fact that GaN has been studied far more extensively than the other group
III nitrides, further investigations are still needed to approach the level of understanding
of technologically important materials such as Si and GaAs. GaN growth
often suffers from large background n-type carrier concentrations because of native
defects and, possibly, impurities. The lack of commercially available native substrates
Table 1.20 Parameters related to thermal properties of wurtzitic InN (in part after Ref. ).
aTSFC: thermodynamic state function changes.
exacerbates the situation. These, together with the difficulties in obtaining p-type
doping, and the arcane fabrication processes caused the early bottlenecks stymieing
progress. Information available in the literature on many of the physical properties of
GaNis in some cases still in the process of evolution, and naturally controversial. This
Table 1.21 Parameters related to electrical and optical properties
of wurtzitic InN (in part after Ref. ).
Table 1.22 Available parameters for mechanical for zinc blende InN.
Table 1.23 Available electrical and optical properties of zinc blende InN, primarily calculated.
is in part a consequence of measurements being made on samples of widely varying
quality. For this book, when possible we have disregarded the spurious determination.
However, measurements are too few to yield a consensus, in which case the
available data are simply reported.
The burgeoning interest in nitrides has led to substantial improvements in the
crystal growth and processing technologies, thus overcoming many difficulties encountered
earlier. Consequently, a number of laboratories consistently obtained highquality
GaN with room-temperature background electron concentrations as low as
5 · 1016cm3.Thesuccessfuldevelopmentof approaches leadingto p-typeGaNhas led
to the demonstration of excellent p–n junction LEDs in theUV, violet, blue, green, and
even yellowbands of the visible spectrumwithbrightness suitable foroutdoor displays,
CWlasers, and UVdetectors, including the ones for the solar blind region. Moreover,
powermodulationdopedfield effect transistors(MODFETs) alsogenerically referredto
as heterojunction field effect transistors (HFETs) have been developed. What follows
reports on the state of knowledge regarding the physical properties of GaN.