Band Structure and Properties of InN and In-rich In1-xGaxN Alloys
|Wladek Walukiewicz 2, Kin M. Yu 2, Sonny X. Li 2,3, Rebecca E. Jones 2,3, Joel W. Ager III 2, Eugene E. Haller 2,3, Hai Lu 1, William J. Schaff 1|
1. Cornell University, 425 Philips Hall, Ithaca, NY 14853, United States
In this presentation we review the results of our recent studies aimed at understanding the electronic structure and its effects on electrical and optical properties of InN and In-rich In1-xGaxN alloys. We have investigated MBE-grown films, unirradiated as well as irradiared with high energy particles. Measurements of the fundamental absorption edge give the value of 0.64 eV for the room temperature energy gap of InN. The low energy gap and a strong kp interaction leads to a small electron effective mass and a distinctly nonparabolic conduction band. In samples with high electron concentrations, a large increase in the absorption edge energy is observed due to the Burstein-Moss shift. In addition to having a narrow gap, InN also has an extremely high electron affinity of 5.8 eV, which places the conduction band edge of this material 0.9 eV below the average energy of dangling bond defects represented by the Fermi level stabilization energy, EFS. This unusual band alignment explains the extreme proclivity for n-type conduction and the large surface electron accumulation densities in InN and In-rich alloys. As grown, undoped InN is always n-type with electron concentrations ranging from mid 1017 cm-3 to as high as 1021 cm-3. A similar range of electron concentrations can be achieved by irradiation with 2 MeV He+ ions. At a sufficiently high dose, the electron concentration saturates. In agreement with the amphoteric defect model the saturation concentration ns, corresponds to Fermi energy pinned at EFS. In In1-xGaxN the conduction band shifts towards the EFS resulting in reduced ns with increasing x. For x>0.66 EFS moves below the conduction band edge and acceptor like defects are preferentially formed, leading to a decrease of electron concentration in irradiated samples. Photoluminescence results show that samples with x<0.6 are two orders of magnitude less sensitive to irradiation damage than standard III-V compounds.
[ABSTRACT TRUNCATED TO 2000 LETTERS]
Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium A, by Wladek Walukiewicz
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-19 18:20 Revised: 2009-06-07 00:44