Effects of stoichiometry on electrical, optical, and structural properties of indium nitride

A series of indium nitride (InN) epilayers with different excess indium (In) concentration are grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire substrates. The increasing excess In concentration of the epilayers correlates with an increasing free-electron concentration and a decreasing electron mobility. Photoluminescence (PL) illustrates a 0.77-0.84 eV transition for all samples with a redshift in the peak energy with increasing In concentration (for the highest free-electron concentration of 4 x 10(21) cm(-3)). This suggests that the similar to 0.8 eV PL transition is not consistent with the band-edge transition in InN. Moreover, an additional PL transition at 0.75 eV along with the In clusters observed in transmission electron microscopy analysis are found only in the 29% excess In sample. This implies a relationship between the new PL transition and the presence of In clusters. Finally, secondary-ion mass spectrometry is used to verify that the contamination, especially hydrogen (H) and oxygen (O) impurities, has no influence on the redshift of the similar to 0.8 eV PL peaks and the existence of the additional 0.75 eV peak in the sample containing In clusters. (c) 2005 American Institute of Physics.