Deep level defects in Ga- and N-polarity GaN grown by molecular beam epitaxy on si(111)

Deep level transient spectroscopy has been used to characterize the deep level traps in Ga- and N-polarity GaN films grown by plasma assisted molecular beam epitaxy on Si(111) substrate. The two deep level traps at E _c-E_t∼0.21 eV (E1) and E_c-E _t∼0.48 eV (E₂) have been detected in Ga-polarity GaN. The E1 level commonly observed deep trap related to the nitrogen vacancy in GaN. It is found that, the E₂ level exhibits logarithmic capture kinetic behavior and substantially increases its capture cross section from 10 ^-15 to 10^-12 cm² by employing different pulse width ranging from 5 ms to 35 ms. Such behavior of E₂ trap with filling pulse length attributes that, the trap is originated from threading dislocations. In case of N-polarity GaN, we observed two deep level traps with activation energies of E_c-E_t∼0.53eV (E3) and E _c-E_t∼0.89eV (E₄). The estimated capture cross-sections (σs) for these defects were found to be ∼2.51×10^-15cm² and ∼5.21×10 ^-16cm² respectively. The E3 and E₄ are nitrogen antisite point defect and extended defect related to dislocation deep levels, results from growth on N-polarity crystal structure. Crown