**5.4.3 Application of solar and the other**

Due to physical nature and peculiarities of generation of the inverse *p-n* junction its application is the easiest and the most efficient in those semiconductor technologies, which involve the development of two-dimensional (flat) *p-n* transitions over a considerable square [67]. Solar cells are related to the devices of such a type. Further development of these investigations will lead to the new technology of *p-n* junction formation in silicon, providing simplification and cost reduction of production process of solar cells and another various semiconductor devices.

## **5.5 The development of III-V heterostructures for solar cells**

The following four types of heterostructures based on InGaAsP compounds have been developed for solar cells by means of MOGPE using Aixtron AIX 200RF installation and capillary epitaxy technique under improved conditions and by using the refined technologies of the epitaxial growth on GaAs substrates of *n-* and *p-*types of conductivity:


that any 'encounter' of a self-interstitial with the boron atoms immediately leads to the boron displacement into the interstitial state), the coefficient a/D ratio would be equal to 4r=4 x 10-7 cm, where r is of the order of the interatomic distance. The difference between the two

*A possibility of long-range migration of interstitial boron.* It was assumed in the above discussion that the boron atoms displaced into interstitial state do not diffuse much from the initial location. The alternative possibility is that the Bi species are of high mobility (comparable to the self-interstitial mobility), and therefore they can migrate to the distance comparable to the sample thickness. In this case, a considerable spatial redistribution of boron impurity would occur. The final profile of Bi would be smoothed by diffusion to some constant (depth-independent) concentration Ni. The mass-action law would then imply that the substitutional boron concentration, Ns = NiK/C, is inversely proportional to C(x). Therefore, substitutional boron would accumulate near the back surface, where C(x) is at minimum. Such a profile of substitutional impurity (with a well-pronounced accumulation at the back

A formation of triple junction (Fig. 29 b) can be accounted for by the long-distance migration of Bi. The boron profile after the first irradiation is of the type shown in Fig. 30 b (t=t2), with just one junction. The second (back-side) irradiation creates an *n*-region near the back surface, and also results in the boron acceptor accumulation near the front side (now nonirradiated). Then a region adjacent to the front side becomes again of *p*-type conductivity.

Due to physical nature and peculiarities of generation of the inverse *p-n* junction its application is the easiest and the most efficient in those semiconductor technologies, which involve the development of two-dimensional (flat) *p-n* transitions over a considerable square [67]. Solar cells are related to the devices of such a type. Further development of these investigations will lead to the new technology of *p-n* junction formation in silicon, providing simplification and cost reduction of production process of solar cells and another various

The following four types of heterostructures based on InGaAsP compounds have been developed for solar cells by means of MOGPE using Aixtron AIX 200RF installation and capillary epitaxy technique under improved conditions and by using the refined technologies of the epitaxial growth on GaAs substrates of *n-* and *p-*types of conductivity: 1. *p-*GaAs substrate, 2.7 μm absorption range, InGaP window - 0.2 μm, contacting layer

2. *p-*GaAs substrate, InGaP barrier layer - 0.03 μm, 3 μm – GaAs absorption range, InGaP

3. **n**+*-* GaAs substrate, barrier InGaP - 0.2 μm, absorption range - undoped GaAs 3 μm, emitter *- p-*GaAs - 0.4 μm, *p-*InGaP window- 0.02 μm, contacting layer p-GaAs - 0.4 μm; 4. n+*-* GaAs substrate, buffer n+-GaAs-0.6 μm; barrier n+-InGaP-0.05 μm; absorption layer undoped GaAs-3.3 μm; emitter p+-GaAs-0,07 μm; window p+- InGaP0,07 μm;

contacting layer p++-GaAs-0.2 μm; antireflecting layer fianite-0.1 μm;.

numbers indicates some kinetic barrier (roughly, 0.25 eV) for the kick-out reaction.

surface) is typical during in-diffusion of Au and Pt impurities [65, 66].

**5.5 The development of III-V heterostructures for solar cells** 

window - 0.06 μm, contacting layer – 0.6 μm;

The resulting structure is *p–n–p–n* (Fig. 29b, d).

**5.4.3 Application of solar and the other** 

semiconductor devices.

GaAs – 0.2 μm;

Prototypes of the solar cells have been manufactured using the obtained samples. Fianite films were used as antireflecting and protective coatings [68, 69]. The films were deposited by means of magnetron sputtering (Fig. 31).

The study of characteristics of the prototypes of the heterostructure solar cell has shown 20- 30 % efficiency gain due to the application of the fianite antireflecting films.

Fig. 31. Prototype sample of the heterostructure solar cell of 40x40 mm size supplied with fianite antireflecting coating: functional side with Au contacting routs (a), reverse side with Au+Ti contacting layer (b)
