**4.2.3 Deep N-H related acceptor state H2**

The ionized acceptor density (*N*A) is found to be in good linear dependence with N concentration in *p*-type GaAsN samples (see Fig. 12 (a)). As given in Figs. 12(b) and (c), the junction capacitance (*C*j) showed a *N*-related sigmoid behavior with temperature in the range 70 to 100 K. This behavior has not yet been observed in GaAs and *n*-type GaAsN grown by CBE. It was recorded at 20 K in silicon *p-n* junction and explained by the ionization of a shallow energy level (Katsuhata, 1978; 1983). Hence, the N dependence of *N*<sup>A</sup> and *C*j is explained by the thermal ionization of a *N*-related acceptor-like state. The thermal ionization energy of this energy level was estimated in the temperature range 70 to 100 K to be between 0.1 and 0.2 eV. It is in conformity with the theoretical calculations, which suggested the existence of a N-related hole trap acceptor-like defect with an activation energy within 0.03 and 0.18eV above the VBM of GaAsN (Janotti et al., 2003; Suzuki et al., 2008). Experimentally, a deep acceptor level, A2, was confirmed in CBE grown undoped GaAsN with ionization energies of *E*A1 = 130 ± 20 meV (Suzuki et al., 2008). On the other hand, the properties of *H*2 in N-varying GaAsN schottky junctions are cited below: The peak temperature of *H*2 is within the temperature range of increase of Cj. This means that the electric field at this temperature range fellows the same behavior of Cj and depends on N concentration. Hence, the emission of carriers from the charged traps is affect by the Poole-Frenkel emission (Johnston and Kurtz, 2006). This is confirmed by the fluctuation of *E*H2 from one sample to another depending on N concentration (see Table 3). However, the average of *E*H2 is within the energy range of the acceptor level obtained from theoretical prediction and identical to EA2 (Suzuki et al., 2008; Janotti et al., 2003). Furthermore, as given in Fig. 12 (d), *N*H2-adj is in linear dependence with *N* concentration. Therefore, *H*2 is proved to be the N-related hole trap acceptor-like state, which thermal ionization increased *C*j and

Investigation of Lattice Defects in GaAsN

H2 may be related to the N-H-VGa structure.

**0.1 0.2 0.3 0.4 0.5 0.6**

**[N](%)**

concentration at a growth temperature of 420 C.

undoped *p*-type GaAsN Schottky junctions.

Fig. 13. N dependence of (a) NA and (b) TEGa flow rate dependence of growth rate and N

[N](%) EH2 (eV) H2(cm2) NH2-adj(cm-3) Emax (V/cm) NH2-Cj(cm-3) NH2-Cj/ NA 0.12 0.210 2.8 10-14 2.64 1015 6.2 104 2.23 1015 0.36 0.20 0.150 6.3 10-16 3.08 1015 1.4 105 2.88 1016 0.91 0.34 0.138 6.3 10-16 5.20 1015 2.1 105 6.56 1016 0.93 0.51 0.103 1.3 10-17 9.12 1015 2.3 105 7.55 1016 0.87 Table 3. Summary of EH2, H2, *N*H2-adj, *E*max, *N*H2-est, and the ratio *N*H2-Cj/*N*A for CBE grown

**0.5 1.0 1.5 2.0 2.5 3.0**

**(b)**

**Growth rate (m/h)**

**0.00 0.05 0.10 0.15 0.0**

**TEGa(sccm)**

**0.4**

**0.6**

**0.8**

**[N] (%)**

**1.0**

**0**

**2**

 **N**

**A**

**(x 1016 cm-3)**

**4**

**6**

**8**

**(a)**

**10**

Grown by Chemical Beam Epitaxy Using Deep Level Transient Spectroscopy 507

To investigate the origin of *H*2, it is worth remembering some previous results about carrier concentration and the density of residual impurities in undoped GaAsN grown by CBE, obtained using Hall Effect, Fourier transform infra-red (FTIR), and second ion mass spectroscopy (SIMS) measurements. On one hand, under lower Ga flow rates (TEGa), *N*<sup>A</sup> and *N*H2 sowed a rapid saturation with [*N*], despite the increase of [*N*] (see Fig. 13 (a)). This means that the atomic structure of *H*2 depends on other atoms, either than *N*. In addition, the densities of *C* and *O* was found to be less than free hole concentration, which excludes these two atoms from the origin of *H*2. On the other hand, using SIMS measurements, the ratio [H]TEGa = 0.02/[H]TEGa = 0.1 was evaluated to be 0.6 (Sato et al., 2008). Furthermore, the free hole concentration at room temperature showed a linear increase with the density of *N-H* bonds (Nishimura et al., 2006). This means that *N*A depends strongly on [*H*] and the saturation of *N*A under lower TEGa can be explained by the desorption of *H* from the growth surface, since the growth rate in our films was found to be in linear dependence with TEGa. Hence, the structure of *H*2 is related to the N-H bond. However, the *N-H* bond may not be the exact structure of *H*2 because the slope of the linear relationship between *N*<sup>A</sup> and [*N-H*] increased with increasing growth temperature (TG [400, 430] C). This indicates that *N*A is determined by both the number of *N–H* and another unknown defect, which concentration increased with increasing TG. The binding energy of this unknown defect can be determined from Arrhenius plot. Furthermore, the formation energy of (N-H-VGa)-2 was found to be lower than (N-VGa)-3, (H-VGa)-2, and isolated VGa-3 (Janotti et al., 2003). This means that the unknown defect may be VGa. These predictions were experimentally supported using positron annihilation spectroscopy results (Toivonen et al., 2003). Hence,

drops the depletion region width. The contribution of *H*2 in the background doping of ptype GaAsN films grown by CBE can be evaluated from the ratio between the real NH2-Cj calculated from the change of Cj and *N*A at room temperature (Bouzazi et al., 2010). As shown in Fig. 12 (*e*) and (*f*), This ratio comes closer to the unit for a N concentration greater than 0.2%. Thus, *H*2 is the main cause of the high background doping in *p*-type GaAsN.

Fig. 12. N dependence of (a) *N*A, (c) amplitude of Cj after thermal ionization of *H*2, and (d) NH2-adj. (b) Sigmoid increase of Cj between 70 and 100 K for two different GaAsN samples. *N* dependence of (e) NH2-Cj and (f) NH2-Cj /NA.

drops the depletion region width. The contribution of *H*2 in the background doping of ptype GaAsN films grown by CBE can be evaluated from the ratio between the real NH2-Cj calculated from the change of Cj and *N*A at room temperature (Bouzazi et al., 2010). As shown in Fig. 12 (*e*) and (*f*), This ratio comes closer to the unit for a N concentration greater than 0.2%. Thus, *H*2 is the main cause of the high background doping in *p*-type GaAsN.

Fig. 12. N dependence of (a) *N*A, (c) amplitude of Cj after thermal ionization of *H*2, and (d) NH2-adj. (b) Sigmoid increase of Cj between 70 and 100 K for two different GaAsN samples. *N*

**2**

**0.4**

**0.6**

*N***H2-Cj/N**

**A** (**-**)

**0.8**

**1.0**

**(f)**

*N***H2-adj** **4**

**6**

(**x 1015cm-3**)

**8**

**(d)**

**10**

**0.0**

**0.7**

**Cjunction (x 100pF)**

**1.4**

**75 100 125 150**

**H2 [N] = 0.51% (b)**

**Tempertaure**

**0.1 0.2 0.3 0.4 0.5**

**[N] (%)**

**0.1 0.2 0.3 0.4 0.5**

**[N] (%)**

**[N] = 0.34%**

**0.0 0.2 0.4 0.6**

**[N](%)**

**0.0 0.2 0.4 0.6**

**[N] (%)**

**0.1 0.2 0.3 0.4 0.5**

**[N] (%)**

dependence of (e) NH2-Cj and (f) NH2-Cj /NA.

**0**

**0.0**

**0**

**2**

*N***H2-Cj**

(**x 1016cm-3**)

**4**

**6**

**8**

**(e)**

**10**

**0.3**

**Cj (x 100pF)**

**0.6**

**0.9**

**1.2**

**(c)**

**2**

 **N**

**( x 1016 cm-3)**

**A**

**4**

**6**

**8**

**(a)**

To investigate the origin of *H*2, it is worth remembering some previous results about carrier concentration and the density of residual impurities in undoped GaAsN grown by CBE, obtained using Hall Effect, Fourier transform infra-red (FTIR), and second ion mass spectroscopy (SIMS) measurements. On one hand, under lower Ga flow rates (TEGa), *N*<sup>A</sup> and *N*H2 sowed a rapid saturation with [*N*], despite the increase of [*N*] (see Fig. 13 (a)). This means that the atomic structure of *H*2 depends on other atoms, either than *N*. In addition, the densities of *C* and *O* was found to be less than free hole concentration, which excludes these two atoms from the origin of *H*2. On the other hand, using SIMS measurements, the ratio [H]TEGa = 0.02/[H]TEGa = 0.1 was evaluated to be 0.6 (Sato et al., 2008). Furthermore, the free hole concentration at room temperature showed a linear increase with the density of *N-H* bonds (Nishimura et al., 2006). This means that *N*A depends strongly on [*H*] and the saturation of *N*A under lower TEGa can be explained by the desorption of *H* from the growth surface, since the growth rate in our films was found to be in linear dependence with TEGa. Hence, the structure of *H*2 is related to the N-H bond. However, the *N-H* bond may not be the exact structure of *H*2 because the slope of the linear relationship between *N*<sup>A</sup> and [*N-H*] increased with increasing growth temperature (TG [400, 430] C). This indicates that *N*A is determined by both the number of *N–H* and another unknown defect, which concentration increased with increasing TG. The binding energy of this unknown defect can be determined from Arrhenius plot. Furthermore, the formation energy of (N-H-VGa)-2 was found to be lower than (N-VGa)-3, (H-VGa)-2, and isolated VGa-3 (Janotti et al., 2003). This means that the unknown defect may be VGa. These predictions were experimentally supported using positron annihilation spectroscopy results (Toivonen et al., 2003). Hence, H2 may be related to the N-H-VGa structure.

Fig. 13. N dependence of (a) NA and (b) TEGa flow rate dependence of growth rate and N concentration at a growth temperature of 420 C.


Table 3. Summary of EH2, H2, *N*H2-adj, *E*max, *N*H2-est, and the ratio *N*H2-Cj/*N*A for CBE grown undoped *p*-type GaAsN Schottky junctions.

Investigation of Lattice Defects in GaAsN

292-299.

401-408.

pp. 387-387.

pp. 6403-6406.

pp. 161201-161204.

144.

2064.

881.

Grown by Chemical Beam Epitaxy Using Deep Level Transient Spectroscopy 509

Bouzazi, B.; Nishimura, K.; Suzuki H.; Kojima, N.; Ohshita, Y. & Yamaguchi M. (2010).

Bouzazi, B.; Suzuki, H.; Kojima, N.; Ohshita, Y. & Yamaguchi, M. (2011). Japanese Journal

Bube, R. H. (1956). Comparison of Surface-Excited and Volume-Excited Photoconduction in Cadmium Sulfide Crystals. Physical Review, Vol.101, pp. 1668-1676. Bube, R. H. (1960). Photoconductivity of Solids. John Wiley & Sons, Inc., New York, pp.

Deenapanray, P. N. K.; Tan, H. H. & Jagadish, C. (2000). Investigation of deep levels in

DeVore, H. B. (1959). Gains, response times, and trap distributions in powder

Friedman, D. J.; Geisz, J. F.; Kurtz, S. R.; & Olson, J. M. (1998). 1-eV Solar Cells with GaInNAs Active Layer. Journal of Crystal Growth, Vol.195, pp. 409-415. Geisz, J. F.; Friedman, D. J.; Olson, J. M.; Kurtz, S. & Keyes, B. M. (1998). Photocurrent of 1

Geisz, J. F. & Friedman, D. J. (2002). III–N–V Semiconductors for Solar Photovoltaic Applications. Semiconductor Science and Technology, Vol.17, No.8, pp. 769-777. Hall, R. N. (1952). Electron-Hole Recombination in Germanium. Physical Review, Vol. 87,

Inagaki, M.; Suzuki, H.; Suzuki, A.; Mutaguchi, K.; Fukuyama, A.; Kojima, N.; Ohshita, Y.

Janotti, A.; Zhang, S. B.; Wei, S. H. & Van de Walle, C. G. (2002). Effects of hydrogen on

Janotti, A.; Wei, S. H.; Zhang, S. B. & Kurtz, S. (2003). Interactions between nitrogen,

Jock, M. R. (2009). Effect of N Interstitials on the Electronic Properties of GaAsN Alloy

Johnston, S. W. & Kurtz, S. R. (2006). Comparison of a dominant electron trap in *n*-type

Katsuhata, M.; Koura, K. & Yoshida S. (1978). Temperature Dependence of Capacitance of

Katsuhata, M.; Yamagata, S., Miyayama, Y.; Hariu, T. & Shibata, Y. (1983). P-n Junction

Films. Thesis, the University of Michigan, 2009.

Science & Technology, A24 (4), pp. 1252-1257.

vapor deposition. Applied Physics Letters, Vol.77, pp. 696-698.

rapid thermally annealed SiO2-capped n-GaAs grown by metal-organic chemical

eV GaInNAs lattice-matched to GaAs. Journal of Crystal Growth, Vol.195, pp.

& Yamagichi, M. (2011). Shallow Carrier Trap Levels in GaAsN Investigated by Photoluminescene. Japanese Journal of Applied Physics, Vol.50, 4, pp. 04DP141-

the electronic properties of dilute GaAsN alloys. Physical Review Letters, Vol.89,

hydrogen, and gallium vacancies in GaAs1-xNx alloys. Physical Review B, Vol.67,

and *p*-type GaNAs using deep-level transient spectroscopy. Journal of Vacuum

Silicon p-n Step Junctions. Japanese Journal of applied physics, Vol.17, pp. 2063-

Capacitance Thermometers. Japanese Journal of Applied Physics, Vol.22, pp. 878-

Cell, Current Applied Physics, Vol.10, pp. 188-190.

photoconductors. RCA Review, Vol. 20, pp. 79-91.

of Applied Physics, Vol.49, pp. 121001-121006.

Properties of Chemical Beam Epitaxy grown GaAs0.995N0.005 Homo-junction Solar
