**4. Lattice defects in GaAsN grown by CBE**

494 Solar Cells – New Aspects and Solutions

To formulate the recombination process, we consider the same notation in § 2.1.2, with

 ( ) [ ( )] ( ) [ ( )] *<sup>T</sup> p T pT T Dn T n T T*

 ( ) ( ) [ (0)- ( )]exp(- ) *<sup>T</sup> ip T ip T T T dn t nt n n n*

pulse. Considering the IDLTS and IDC-DLTS the peak heights of the recombination center in

Similarly for hole trap in the *p*-side of a *n+-p* junction, which acts as recombination center,

All GaAsN films were grown by CBE on high conductive *n*- or *p*-type GaAs 2 off toward [010] substrate using Triethylgallium ((C2H5)3Ga, TEGa), Trisdimethylaminoarsenic ([(CH3)2N]3As, TDMAAs), and Monomethylhydrazine (CH3N2H3, MMHy) as Ga, As, and N sources, respectively. The flow rates TEGa = 0.1 sccm and TDMAAs = 1.0 sccm were considered as conventional values. The growth temperatures of 420 C and 460 C were used for *p*-type and *n*-type GaAsN, respectively. Concerning the doping, *p*-type GaAsN films are unintentionally doped. The n-type alloys were obtained using a silane (SiH4)

Three different device structures are used in this study: (*i*) *n*- and *p*-type GaAsN schottky contacts, (*ii*) *n*+-GaAs/*p*-GaAsN/*p*-GaAs, and (*iii*) *n*-GaAsN/*p*+-GaAs hetro-junctions. The *N* concentration in all GaAsN layers was evaluated using XRD method. Aluminum (*Al*) dots with a diameter of 0.5/1 *mm* were evaporated under vacuum on the surface of each sample. Alloys of *Au-Ge* (88:12 %) and *Au-Zn* (95:05 %) were deposited at the bottom of *n*-type and *p*-type GaAs substrates for each device, respectively. Some samples were treated by postthermal annealing under *N*2 liquid gas and using GaAs cap layers to avoid As evaporation from the surface. The temperature and the time of annealing will be announced depending on the purpose of making annealing. The background doping and the doping profile in the extended depletion region under reverse bias condition were evaluated using the capacitance-voltage (C-V) method. The leakage current in all used samples ranged from 0.3

conventional and DC-DLTS, respectively. Equation (11) can be rewritten properly as

*<sup>T</sup>* ( ) ip *DLTS DCDLTS*

*T DCDLTS*

*<sup>T</sup>* ( ) ip *DLTS DCDLTS*

source or by growing the films under lower MMHy and high growth temperature.

*T DCDLTS*

*n t I I*

*N I*

*n t I I*

*N I*

and that only occupied by electrons in the n-side of the junction can be expressed by

where *p* is the average of injected holes. As a solution of Eq. (10), we have

 *ND*. The relationship between the total density of recombination centers

*dn en t pc N n t N cn t e N n t dt* (10)


(12)

(13)

(11)

*p thp ip*

*n thn ip*

*n vt*

*p v t*

assuming that *n* 

where *n*T() = (*pc*p+ *e*n)/(

we obtain

*dt*

 -1*N*T), 

where *n* is the average of injected electrons.

**3. Experimental procedure** 

In this section, the distribution of electron and hole traps in the depletion region of GaAsN grown by CBE will be dressed using DLTS and related methods.
