Surface electronic structure of H/InAs(001)-4×2 studied by synchrotron radiation photoemission spectroscopy
Chien-Wen Chuang (莊茜雯)1, Yi-Ting Cheng (鄭伊婷)2, Tun-Wen Pi (皮敦文)3, Ashish Atma Chainani1*
1Condensed Matter Physics, National Synchrotron Radiation Research Center, Hsinchu City, Hsinchu, Taiwan
2Grad. Inst. of Appl. Phys. and Dept. of Physics, National Taiwan University, Taipei, Taiwan
3Nano Science Group, National Synchrotron Radiation Research Center, Hsinchu, City, Hsinchu, Taiwan
* Presenter:Ashish Atma Chainani,
The free surface electronic structure of undoped and n-type InAs(001) is well-known to exhibit electron accumulation while p-type InAs(001) is known to show an inversion layer on the surface [1,2]. Further, the equilibrium surface Fermi level of InAs(001) is known to be pinned ~0.15 eV above the conduction band minimum [3,4]. In this work, we carry out a comparative study using high-resolution synchrotron radiation (hν = 40 - 160 eV) photoemission to clarify the effects of hydrogenation on the electronic structure of undoped, S (electron)-doped, and Zn (hole)-doped InAs(001). Upon annealing the chemically treated samples at 420°C, the surfaces show a clear 4×2 reconstruction [5], and a highly surface-sensitive scan of the In 4d (As 3d) core level using 100 eV photon energy exhibits well-resolved spin-orbit split states. A detailed fitting analysis reveals a single component surface contribution with surface core-level shifts of less than 200 meV in both the In 4d and As 3d core-level spectra. The In (As) surface component appears in an energy position higher (lower) than the bulk, which suggests that a charge redistribution occurs in the surface In and As atoms. The core-level behavior of InAs(001)-4×2 is very similar to that of InGaAs(001)-4×2 and distinct from that of GaAs(001)-4×2. Nevertheless, the magnitude of the surface core-level shifts in InAs(001) are smaller than that in InGaAs(001) due to different reconstructed configurations. In InGaAs, the surface In lies in the same plane as As to form As-In-As configuration, while in InAs, the surface In protrudes upwards to form a triangular bond with the two As atoms positioned underneath.
Upon exposure of InAs(001)-4×2 to atomic hydrogen (H+ and H) generated by a UHV cracker, the valence band maximum undergoes a shift to higher binding energies, suggestive of n-type doping. The surface-related feature gradually drops in intensity with increasing hydrogen dosages. Concurrently, the surface components in both In 4d and As 3d core-level spectra shows a reduction in strength with appearance of Hydrogen-induced components. Interestingly, the induced In 4d component shows up in the low binding energy region, while the induced As 3d component appears in the high binding energy region of the main peaks. Clearly, the cracked H atom is associated with the surface In atom and the H+ atom with the surface As atom. The results suggest that the surface In atoms get charge enriched upon H bonding, and the like cause of a re-transformation from InAs(001)-4×2 to the original InAs(1x1) structure as confirmed by LEED measurements.
References :
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Keywords: Surface reconstruction, Synchrotron photoemission, Electronic structure, Hydrogenation of InAs