Abstract:
Cathodoluminescence (CL) spectra from silicon doped and undoped wurtzite n-type GaN have been
measured in a SEM under a wide range of electron beam excitation conditions, which include accelerating
voltage, beam current, magnification, beam diameter, and specimen temperature. The CL intensity dependence
on excitation density was analyzed using a power-law model (ICL infinity Jm) for each of the observed CL bands in
this material. The yellow luminescence band present in both silicon and undoped GaN exhibits a close to cube
root (m=0.33) dependence on electron beam excitation at both 77 K and 300 K. However, the blue (at 300 K)
and donor-acceptor pair (at 77 K) emission peaks observed in undoped GaN follow power laws with exponents
of m 5 1 and m 5 0.5, respectively. As expected from its excitonic character, the near band edge emission
intensity depends linearly (m 51) in silicon doped GaN and superlinearly (m 51.2) in undoped GaN on the
electron beam current. Results show that the intensities of the CL bands are highly dependent not only on the
defect concentration but also on the electron-hole pair density and injection rate. Furthermore, the size of the
focussed electron beam was found to have a considerable effect on the relative intensities of the CL emission
peaks. Hence SEM parameters such as the objective lens aperture size, astigmatism, and the condenser lens
setting must also be considered when assessing CL data based on intensity measurements from this material.
