Electronic properties of vacancy related defects in ZnO induced by mechanical polishing

Abstract

Electronic properties of defects induced by mechanical polishing in hydrothermally grown n-type ZnO have been investigated by capacitance versus voltage measurements and deep level transient spectroscopy (DLTS). The DLTS measurements have been performed in the temperature range 80-600 K enabling exploration of deep-level states in the vicinity of the middle of the energy bandgap. The results show that mechanical polishing forms defects in the near surface region which strongly compensate and/or passivate the dominant shallow donors. Two pronounced polishing-induced defects are revealed with energy level positions around 1.0 eV and 1.2 eV below the conduction band edge. These levels are assigned to vacancy-related defect centers and substantially reduced in strength by post-polishing etching in diluted hydrofluoric acid.

Oxygen vacancy andEC− 1 eV electron trap in ZnO

“…The energy level reported by Quemener et al [21] for the E5 trap is in good agreement with our results and seems to be also the V O , except that the capture cross section is slightly lower. Unfortunately, the Arrhenius diagram has not been shown, preventing the detailed comparison with the five Arrhenius diagrams reported in the present work.…”

“…Some works [10][11][12][13][14] mentioned levels with such low energy but larger capture cross sections except in [15,16]. The trap E500 observed in sample #2 and #4 is often reported in literature [17][18][19][20][21] and commonly named E4 even if its attribution is still unclear. The trap E640 has been observed only in samples #1 and #2, which are two CVT grown samples.…”

Deep levels and acceptors in Zn(Mg)O: effect of N-doping

“…With an energy around 300 meV below the CBM, it has been reported that indeed two levels very close in energy can lead to the observed peak (Auret et al report energies of 300 meV and 370 meV [7]). This level has been observed largely among the existing literature, with very similar energy values [29,115,[140][141][142].…”

“…Contrarily to E2, this level has shown in annealing experiments to be related to Zn-rich conditions [117], and even H-related [95]. Several reports have shown similar energies and capture cross sections [29,48,115,140], with the most recent study, dedicated entirely to this defect having been performed by Hupfer et al [49]. They analyze the influence of H during the formation and annihilation of this defect, although the attribution they suggest is the oxygen vacancy (V O ).…”

“…its parameters can be calculated and obtain an activation energy around 100 meV below the CBM, with a capture cross section σ n = 4 × 10 −18 cm −2 . However, many groups have published levels labeled as E2, with different activation energies (0.18 eV [115] and 0.19 [114]). In annealing experiments, this level has been proved to be related to O-rich conditions, although no clear attribution has been made.…”