In this paper, promising experimental results for the p-type electrical properties of carbon-doped (C-doped)
AlGaN are discussed. P-type conductivity was experimentally achieved in C-doped (0001) plane AlGaN layers
with from a small amount to 55% solid Al composition, but not in (0001) plane GaN. The maximum free hole
density (determined by van der Pauw geometry-Hall effect measurement) achieved for an AlGaN layer with 10%
solid Al composition was p= 3.2 x 1018 cm-3. The maximum net ionized acceptor densities (NIAD = (NA
which were determined by capacitance-voltage measurement, for AlGaN with 6, 10, 27, and 55% solid Al
compositions, were all in the range of (3-7) x 1018 cm-3. Moreover, the electrical activity of the carbon acceptors
was estimated to be 55-71% from the NIAD and secondary-ion microprobe mass spectrometry analysis data on
the carbon concentration. Activation energy of carbon acceptors was estimated to be 22-30 meV from this
electrical activity. On the other hand, optical property of C-doped AlGaN was compared with undoped AlGaN.
Then we found new emission, which related to carbon acceptors, at smaller energy side by 29-35 meV from band
edge-emission of the AlGaN. A p-n junction was also fabricated using the C-doped p-type AlGaN.