| Abstract Scope |
<p>Incorporating only 0.5% of N into GaP changes the indirect-bandgap GaP to direct-bandgap GaNP due to the strong interaction between N localized states and GaP extended states[1]. The dilute nitride GaNP is unique among the common semiconductors in that it has a large bandgap bowing[2] and its bandgap can cover a wide range of solar spectrum for a relatively small amount of nitrogen incorporation. In addition, the GaN<sub>x</sub>P<sub>1-x</sub>/GaN<sub>y</sub>P<sub>1-y</sub> junction has type-II bandgap alignment where photoexcited electron-hole pairs are separated by the built-in potential. The GaN<sub>x</sub>P<sub>1-x</sub>/GaN<sub>y</sub>P<sub>1-y</sub> core/shell coaxial nanowires(NWs) have the following merits for photovoltaic application: 1) NWs increase light scattering, enhancing light absorption; 2) The radius of the core can be less than the minority carrier diffusion length, reducing minority carrier recombinations; 3) The nanoscale dimensions also relax lattice-match requirement, making it possible to grow dislocation-free NWs.</p>
<p>We have studied the growth of GaP and GaP/GaNP core/shell NWs on Si(111) substrate by GSMBE. We report for the first time that catalyst-free uniform vertical GaP/GaNP core/shell NWs are successfully grown, with GaP core as the skeleton overcoming the reactive N plasma interference on vapor-liquid-solid mechanism[3] during NW growth at the beginning. Both GaP and GaP/GaNP NWs are hexagonal in shape, following the Si <111> crystal orientation. The GaP NWs are, on average, 110nm in diameter while the GaNP shell layer is averagely 110nm in thickness. GaP and GaP/GaNP NWs are dry-transferred to another Si substrate on which photoluminescence (PL) measurement is performed. Strong room temperature PL at 300K and extremely intense low temperature PL at 44K that both can be seen by naked eyes are observed on GaP/GaNP core-shell NWs ensembles. Around 3% of nitrogen composition in the shell is determined by the band anti-crossing model[4].</p>
Reference:<br>
[1] H.P. Xin, C.W. Tu, Y. Zhang and A. Mascarenhas, Appl. Phys. Lett. 76, 1267 (2000).<br>
[2] W.G. Bi, C.W. Tu, Appl. Phys. Lett. 69, 3710 (1996).<br>
[3] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4, 89 (1964).<br>
[4] W. Shan, W. Walukiewicz, K. M. Yu, J. Wu, J. W. Ager, E. E. Haller, H. P. Xin, and C. W. Tu , Appl. Phys. Lett., 76, 3251 (2000).<br> |