English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Open

Presents the pdf analysis as premium feature

PDF Analysis

Insights

Presents the summarisation as premium feature

Summarisation

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Molecular beam epitaxy of GaNAs alloys with high As content for potential photoanode applications in hydrogen production S. V. Novikov, I C. R. Staddon, and C. T. Foxon School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom K. M. Yu, R. Broesler, M. Hawkridge, Z. Liliental-Weber, and W. Walukiewicz Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720-8197 J. Denlinger Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720-8197 I. Demchenko Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720-8197, Department of Chemistry, University of Nevada Las Vegas, 4505 Maryland, Pkwy-Box 454003, Las Vegas, Nevada 89154-4003, and Institute of Physics, PAS, al. Lotnikow 32/46, 02-668 Warsaw, Poland The authors have succeeded in growing GaN 1âx As x alloys over a large composition range I0 I½ x I½ 0.8I by plasma-assisted molecular beam epitaxy. The enhanced incorporation of As was achieved by growing the i¬lms with high As 2 i¬ux at low Ias low as 100 Â° CI growth temperatures, which is much below the normal GaN growth temperature range. Using x-ray and transmission electron microscopy, they found that the GaNAs alloys with high As content x I¾ 0.17 are amorphous. Optical absorption measurements together with x-ray absorption and emission spectroscopy results reveal a continuous gradual decrease in band gap from I³3.4 to I½1 eV with increasing As content. The energy gap reaches its minimum of I³0.8 eV at x I³ 0.8. The composition dependence of the band gap of the crystalline GaN 1âx As x alloys follows the prediction of the band anticrossing model IBACI. However, our measured band gap of amorphous GaN 1âx As x with 0.3I½ x I½ 0.8 are larger than that predicted by BAC. The results seem to indicate that for this composition range the amorphous GaN 1âx As x alloys have short-range ordering that resembles random crystalline GaN 1âx As x alloys. They have demonstrated the possibility of the growth of amorphous GaN 1âx As x layers with variable As content on glass substrates. I. INTRODUCTION The direct conversion of sunlight into hydrogen by pho- toelectrochemical IPECI water splitting is one of the direct methods to transfer solar energy into a storable fuel. 1 PEC cells use photoactive electrodes immersed in an aqueous electrolyte or water. The choice of material for the photoan- ode is crucial for efi¬cient hydrogen production using the PEC method. The photoanode material needs to be corrosion resistant for prolonged operation. The band gap of semicon- ductor materials used for photoanodes must be at least 2.0 eV IRef. 1I but small enough to absorb most sunlight. In addition to choosing the correct band gap, the conduction and valence band edges must âstraddleâ the H + / H 2 and O 2 / H 2 O redox potentials so that spontaneous water splitting can occur. Gallium nitride IGaNI is a good candidate for this application since it has a band gap of I³3.4 eV, high me- chanical hardness, and high chemical stability. 2 Moreover, the band gap of GaN can be adjusted and decreased due to strong negative bowing in the GaN-based solid solutions with group V elements. 3 Therefore, we suggest that the GaN 1âx As x material system is one of the most promising choices for the photoanodes. Recently, it has been demonstrated that the electronic structure of the conduction or valence bands of alloys with anions of very different electronegativity can be well de- scribed by the band anticrossing IBACI model. 4 Due to the substantial difference in the ionization energies of the As and N anions, the p states of the substitutional As atoms are resonant near the valence band edge of GaN, allowing them to interact strongly with the extended p states of the host. The interaction splits the valence band into a series of E + and E â subbands with dispersion relations that are dependent on the As concentration. 3,4 As a result, this effectively reduces the band gap and pushes the valence band edge up toward the O 2 / H 2 O potential, while leaving the conduction band above the H + / H 2 potential. On the other hand, in the As-rich GaNAs alloys, the hybridization of the localized N s states with the GaAs extended s states gives a strong decrease in the conduction band edge. These two effects cause the large bowing across the entire composition range of the GaâNâAs