Density of states distribution in AlN films measured by CPM and DLTS

Aluminium nitride films are prepared by radio frequency magnetron sputterin g of pure aluminium target in argon-nitrogen-hydrogen mixture at the differ ent value of the nitrogen-hydrogen flow rates. The argon flow rate and part ial pressure are fixed. Nominal substrate temperature is equal to 275 degre esC, glass and silicon wafers are used as substrates. Constant photocurrent method (CPM) and deep level transient spectroscopy (DLTS) are used for the density of electron states (DOS) distribution parameters investigations in the energy ranges which include nearly all AlN band gaps. The CPM is appli ed for experimental investigations of optical absorption coefficient and th e DOS spectra in the 1.4-5.0 eV range. The DOS peaks are found at the energ ies of 2.2-2.7 and below 1.8 eV from the conduction band bottom. The second peak is attributed to the N-Al antisite defects, whereas data on the first one has not been previously reported. Capacitance DLTS technique is used f or the N(E) investigation in the energy range up to 0.85 eV below the condu ction band bottom. Relatively narrow (15-150 meV halfwidth) peaks are found in the energy range. These peaks appearance is attributed to the nitrogen vacancy triplet. The conduction band tail slope characteristic energy is es timated as 25 +/- 10 meV. (C) 2001 Elsevier Science B.V. All rights reserve d.