Effect of H implantation on lattice defects in GaAsN

GaAsN films were treated by H implantation. This experiment was used because H bounds strongly to N in GaAsN films to form N-H complexes (Suzuki et al., 2008; Amore & Filippone, 2005). H ions with multi-energy from 10 to 48 keV were implanted into GaAsN layers with peaks concentration of 5 x 1018 (GaAsNHD1) and 1 x 1019 atom/ cm3 (GaAsNHD2),

image551
image552

respectively. The depth of implantation was thought to be distributed between 110 and 410 nm from the surface of GaAsN by calculating the SRIM 2003 simulation code (Ziegler, 1985). After implantation, the samples were treated by post thermal annealing at 500 °C for 10 min under N2 gas and GaAs cap layers. As plotted in Fig. 7(a) and (b), the crystal quality of GaAsN films after implantation was controlled using XRD curves and C-V measurements. DLTS spectra of implanted samples are shown in Fig. 7(c). After implantation, £1 was not observed; however, two new lattice defects appeared. The signature and the density of these traps are summarized in Table 1. The thermal emission from them is plotted as an Arrhenius plot in Fig. 7(d).

GaAsN

Traps

Ea(eV)

a (cm2)

Nt-adj(cm-3)

Possible origin

As grown

E1

Ecm-0.331

5.18 x10-15

3.37 x1017

(N-As)as

Implanted

EP1

Ecm-0.414

8.20 x10-13

5.88 x 1017

EL5 in GaAs

HP1

Evm-0.105

5.42 x10-18

1.84 x 1016

N-H-VGa

Table 1. Summary of Ea, a, adjusted Nt-adj, and possible origin of defects in as grown and implanted GaAsN samples.

Fig. 7. (a)DLTS spectra of as grown and implanted GaAsN and (b) their Arrhenius plots.

The new electron trap (£P1) is located approximately 0.41 eV below the CBM of GaAsN. Its properties are identical to that of the native defect £L5 in GaAs (Reddy, 1996). Its atomic structure was discussed in many publications, where the common result indicated that £L5 is a complex defect free from impurities and dominated by As interstitials, such VGa-Asi or AsGa-VGa (Deenapanray et al., 2000; Yakimova et al., 1993). The second new defect is a hole trap (HP1) at approximately an average activation energy 0.11 eV above the VBM of GaAsN. Compared with majority carrier traps in GaAs grown with various techniques, no similar hole trap to HP1 was reported. However, in p-type GaAsN grown by CBE with around the same N concentration, £HP1 and aHP1 are identical to that of the hole trap HC2 in p-type GaAsN grown by CBE (bouzazi et al., 2011). This defect was confirmed recently to be an acceptor state in GaAsN films (see § 4.2.3) and to be related to the N-H bond. While the H impurity was provided by implantation, the N atom can originate through two possibilities: First; examining XRD results, the N atom can originate from its ideal site. However, [N] in as grown is much higher than that in implanted samples (~1019 cm-3). It is also much higher than NHP1. Second, N atom can be originated from the complete dissociation of £1, since the
ratio Nei/Nhpi is less than 2. If £1 is the split interstitial (N-N)as/ Nhpi must be at least equals to that of £1 and one N atom remains free. This expectation is disapproved by DLTS measurements, where NHP1 is largely less than NE1. This means that £1 contains only one N atom in its atomic structure. Considering the results of last sub-section, £1 may be the split interstitial (N-As)As formed from one N and one As in a single As site. This result is supported by the theoretical calculation (Zhang et al., 2001).

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