US Team Delivers Evidence For P-doped InN
A partnership between Lawrence Berkeley National Laboratory, Cornell University and the University of California, Berkeley, claims that it has produced the first evidence for p-doping in InN films ( Phys. Rev. Lett. 96 125505).
The work could aid the development of solar cells, LEDs, and laser diodes based on the AlInN material system that has an exceptionally wide direct band gap range (0.7-6.2 eV). n-type InN growth is already established, but p-type material is also needed for device fabrication.
The team grew the 500 nm-thick InN films on sapphire substrates and a 200 nm-thick GaN buffer layer using MBE and a magnesium dopant.
Various techniques were used to establish the film's p-type doping, but in each case the measurements were hampered by n-type conductivity of the surface accumulation layer.
According to the team their experiments showed that their InN films had a net concentration of acceptors in the bulk material below the surface, but the measurements could not verify the presence of free holes.
Capacitance-voltage measurements were used to infer that the film's magnesium-doping level was "in the low 1019 cm-3 range", which suggests that 1-10% of the magnesium dopant atoms act as acceptors.
Transport and photoluminescence measurements provided additional evidence for p-type doping in InN. For example, photoluminescence intensity measurements showed that a dose of helium ions could offset the affect of p-type acceptors introduced by magnesium-doping.
Cornell University's William Schaff said that the team has recently developed techniques that reduce the affect of the n-type surface accumulation layer, which will aid the researchers development of AlInN-based solar cells.