**3. Conclusion**

*Nanowires - Recent Progress*

respectively as given in **Figure 3**.

higher *J*sc value of 2.82 mA/cm2

and 100 nm active layers are obtained for CSS-NW, ND and planar structure

**Figure 4** shows the current density-voltage-power density (J-V-P) curve of n-GaN/ i-In0.1Ga0.9N/p-GaN planar, ND and NW type solar cell. The optimized thickness of 100 nm, 150 nm and 180 nm i-InGaN is considered for all performance analysis. It shows a higher Jsc in CSS-NW as compared to ND and planar structure. It is anticipated that higher current in CSS-NW solar cell is mainly due to higher active absorption region and efficient carrier separation. It is important to highlight that planar and ND type solar cells shows a stair-case type *J-V* curve, which is not there in CSS-NW. It is may be due to low degree of strain relaxation or higher stress generation along the interface which is again related to structural issues of device. Hence, it is always important to engineer the device structure as per the material properties of the absorber layer. High defect density along the interface is also play a major role for low current in planar and ND solar cell. CSS-NW do not possess a staircase J-V curve due to low defect density, low stress and high degree of strain relaxation. It is also observed that the depth of stair-case in *J-V* curve is increasing with higher 'In' contents. Additionally,

is noted in CSS-NW solar cell (**Figure 5**).

It is also observed that due to high degree of strain relation, low defects density and more active area of absorption, CSS-NW structure can accommodate higher thickness of active InGaN layer (W) region. Moreover, higher thickness of absorber enhances the probability of more absorption of photons from sunlight. In other hand, active region of planar and ND type solar cells cannot be increased due to are limitation of surface recombination arte, polarization induced electric field, low degree of strain relaxation and defect density. Voc of ND type solar cell is seen to be higher than CSS-NW type solar cell which is may be due to the recombination rate along the junction. However, the rate of increase in Jsc of CSS-NW structure is comparatively higher than ND and planar solar cell. Similarly, planar solar cell possesses a low as compared

*Current density (black line) – Voltage – Power density (red line) of (a) planar (b) ND and (c) CSS-NW* 

*Open circuit voltage, Voc at 10%, 20%, and 30%, 'In' content for (a) planar (b) Nanodisk and (c) CSS-NW* 

*solar cell at 100 nm, 150 nm, and 180 nm i-InGaN thickness respectively.*

**88**

**Figure 5.**

**Figure 4.**

*solar cell.*

In this chapter, the importance of nanowire solar cell with III-Nitride material is explored in a detailed manner. A comparative analysis is carried out with planar, nanodisk and nanowire type solar cell and concluded that nanowire type structure shows a better performance as compared to others. Additionally, it is found that nanowires in InGaN materials are grown either in triangular or hexagonal orientation. The strain relaxation is more in CSS-nanowires which in turns leads to low in-house defect density along the interfaces. CSS-NWs are also able to accommodate higher thickness of intrinsic material due to high carrier diffusion length. Radial separation of carriers also provides more surface area and better control on carrier separation mechanisms. Hence, it is concluded that radial growth of nanowire provides a broad range of opportunity for performance enhancement of solar cell. The similar type of observation are also applicable to LASER and light emitting diodes, where III-Nitride materials are used.
