4.2 Hole traps in GaAsN grown by CBE

4.2.1 DLTS spectra and properties of hole traps in GaAsN

Here, we only focus on the hole traps that coexist in all p-type GaAsN based Schottky junctions and n+-GaAs/p-GaAsN heterojunction. The difference between these two structures is the temperature range in which the DLTS measurements can be carried out due to the freeze-out of carriers. The DLTS spectrum of p-type GaAsN in the heterojunction is shown in Fig. 8(a). Three hole traps H0, H2, and H5 are observed at 0.052, 0.185, and 0.662 eV above the VBM of GaAsN. Their peak temperatures are 35, 130, and 300 K, respectively. The thermal dependence of emission from the hole traps is plotted as an Arrhenius plot in Fig. 8(b). The activation energy, capture cross section, and density are given in Table 2.

image553

Fig. 8. (a) DLTS spectra of p-type GaAsN grown by CBE and (b) their Arrhenius plots.

The hole traps H2 and H5 were also observed in Schottky junctions and coexist in all samples. H2 is a N-related acceptor-like state and was proved to be in good relationship with high background doping in GaAsN films. These properties will be discussed later. The

hole trap H5 presents the same properties as H3 and HA5 (Li et al., 2001; Katsuhata et al., 1978). It is proposed to be the double donor state (+/++) of EL2 (Bouzazi et al., 2010). The hole trap H0 cannot be observed in Schottky junctions owing to the freeze-out effect.

Traps

Et (eV)

Op(cm2)

Nt-adj(cm-3)

H0

0.052

2.16 x 10-14

4.64 x 1016

H2

0.185

3.87 x 10-17

4.52 x 1015

H5

0.662

6.16 x 10-14

6.24 x 1015

Table 2. Summary of Et, np, and adjusted Nt-adj of H0, H2, and H5.

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