Deep ultraviolet picosecond time-resolved photoluminescence studies of AlN epilayers

Abstract

AlN epilayers with high optical qualities have been obtained by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in AlN epilayers. Two PL emission lines associated with the donor bound exciton (D0X, or I2) and free exciton (FX) transitions have been observed, from which the binding energy of the donor bound excitons in AlN epilayers was determined to be around 16 meV. Time-resolved PL measurements revealed that the recombination lifetimes of the I2 and free exciton transitions in AlN epilayers were around 80 and 50 ps, respectively. The temperature dependencies of the free exciton radiative decay lifetime and emission intensity were investigated, from which a value of about 80 meV for the free exciton binding energy in AlN epilayer was deduced. This value is believed to be the largest free exciton binding energy ever reported in semiconductors, implying excitons in AlN are an extremely robust system that would survive well above room temperature. This together with other well-known physical properties of AlN may considerably expand future prospects for the application of III-nitride materials.

Ultraviolet photoluminescence from Gd-implanted AlN epilayers

“…These defect levels may at the same time provide efficient relaxation channels for energy back transfer to the AlN host. 26 The PL data presented here are quite different than results of CL measurements done on similar Gd-implanted AlN thin films. [20][21][22] While both PL and CL measurements yield an intense UV emission at 318 nm, only the CL measurements have shown evidence of Gd 3+ transitions at other wavelengths, near 259 and 285 nm, arising from higher energy manifolds.…”

Group-II acceptors in wurtzite AlN: A screened hybrid density functional study

“…The binding energy of the free exciton in wurtzite AlN is less than 0.1 eV, so the optical and fundamental band gaps are within 0.1 eV. 32 We found that by varying the screening parameter in the HSE functional to 0.05 from 0.2 1/Å we reproduce the experimental band gap at 0 K but the ionization energies of acceptors also shift up by about 0.25 eV independently of the defect. This would indicate a slight deviation between the calculated and measured thermal ionization energies for Mg defect.…”

Cathodoluminescence study of micro-crack-induced stress relief for AlN films on Si(111)

“…Additional broader peaks were observed at 3.040 and 3.410 eV and were previously related to deep-level oxygen impurities. [14][15][16] Two additional relatively small peaks were observed near 4.5 eV and are likely related to carbon impurities in AlN. 1,14,15 This relatively weak emission demonstrates that only a minor carbon contamination occurred during sample growth.…”

“…[14][15][16] Two additional relatively small peaks were observed near 4.5 eV and are likely related to carbon impurities in AlN. 1,14,15 This relatively weak emission demonstrates that only a minor carbon contamination occurred during sample growth. 16 The depth-resolved analysis of the CL spectra shown in Fig.…”