Intrinsic electron accumulation layers on reconstructed clean InAs(100) surfaces

Abstract

The electronic structures of clean InAs(lOO) surfaces have been investigated by in situ high-resolution electron-energy-loss spectroscopy. Intrinsic electron accumulation layers with carrier densities strongly depending on the surface reconstruction are formed on both As-stabilized and In-stabilized surfaces. The correlation between the surface electron densities and the surface reconstructions suggests that electrons in the accumulation layers are induced by the donorlike intrinsic surface states of InAs whose energy spectrum is determined by the surface reconstructions.It is well known that an electron accumulation layer is easily formed on InAs surfaces. Recently, this surface accumulation layer has attracted much attention because the high density of electrons on the surface has great technological importance, such as the formation of nonalloyed Ohmic contacts 1 and the realization of the three-terminal Josephson devices. 2 It is, however, not clear whether an intrinsic electron accumulation layer is present even on clean InAs (100) surfaces and how it is related with surface atomic configurations.In this work, we studied the electronic structure of both As-stabilized and In-stabilized clean InAs(100) surfaces with in situ high-resolution electron-energy-loss spectroscopy (HREELS). By analyzing the HREELS spectra, it is found for the first time that electron accumulation layers are formed on both As-stabilized and In-stabilized surfaces and, furthermore, that the electron density in the accumulation layer changes reversibly with surface reconstructions. The origin of such electron accumulation layers is discussed.HREELS is a very powerful tool to investigate semiconductor surfaces because it gives us rich information on the surface vibrational excitations which extend into semiconductors by several tens of nanometers. To pursue HREELS measurements, however, it is essential to prepare clean and undamaged semiconductor surfaces. Such techniques as cleaving, 3,4 ion bombardment and subsequent annealing, 5,6 and arsenic deposition 7,8 were used in the previous works. With these methods, however, it is difficult to obtain clean and undamaged InAs(lOO) surfaces with high reproducibility. To overcome this difficulty, the HREELS system is connected with a molecular-beam-epitaxy (MBE) chamber under an ultrahigh-vacuum condition (<3xlO~8 Pa). This configuration keeps the surface contamination negligibly small during measurements [<0.4 L (1 L = 10~6 Torrs) for 2 h] and allows us to investigate clean surfaces.The As-stabilized undoped InAs(100) surfaces were prepared as follows: 0.3-0.5-^um-thick undoped «-type InAs layers were grown on undoped InAs (100) sub-strates by MBE. The bulk electron density in the MBEgrown InAs layer is less than 2xl0 16 cm" 3 . The substrate temperature during the growth was set at 450-490 °C. The As-stabilized surfaces were obtained by cooling the arsenic-stabilized (2x4) reconstructed surfaces down to room temperature in an AS4 flux of -10 15 cm~2s _1 . During the cooling process, the reflec...

Measurement by antilocalization of interactions between InAs surface electrons and magnetic surface species

“…Mobilities and densities vary per sample, yet no significantly systematic variation caused by solution coverage is observed. The values of n s are consistent with previous studies 14,15 . The assignation is confirmed by a self-consistent calculation, using non-parabolicity in the InAs dispersion, with a Γ-point effective mass of 0.024 and low T band gap of 418 meV.…”

“…To extract values for τ s it is advantageous to use a system with pre-existing prominent SOI because the characteristic magnetoresistance of AL shows a turnaround from positive to negative magnetoresistance under increasing B, fa- cilitating unique numerical fits of the AL model to the data. It is well established that at the surfaces of InAs the Fermi level E F is pinned above the conduction band, forming a surface electron accumulation layer and hence a two-dimensional electron system (2DES) at the surface [12][13][14][15] . Our experiments require electrons in close proximity to the local moments, satisfied by the InAs surface 2DES.…”

Photogating in Low Dimensional Photodetectors

“…These study results also could be illustrated by surface band bending, as shown in Figure 2b. InAs has been found to have accumulated electrons on surface and causes downward surface band bending 76, 77, 78. For InAs NW with limited diameter, when under photoexcitation, photogenerated electrons move to the surface and are trapped whereas holes are left in the core and recombine with free electrons, leading to the NPC.…”

Evolution of electron states at a narrow-gap semiconductor surface in an accumulation-layer formation process

“…In addition, the accumulated carrier density depends upon whether the surface is As-stabilized or In-stabilized. 20 At light doping, the accumulation layer becomes distinctly localized near the surface, while, at heavy doping, the accumulation only means that the carrier density in the semi-infinite system becomes enhanced in the neighborhood of the surface. With further increase in doping level, there occurs no substantial accumulation at the surface.…”

“…On the other hand, there are some other EELS measurements on an intrinsic accumulation layer at a clean n-type InAs ͑001͒ surface prepared carefully. 19,20 At light doping, quasi-two-dimensional plasmons occur in a sharply localized accumulation layer, 20 while, at heavy doping, electronic excitations in the accumulation layer are virtually surface plasmons in a semi-infinite system with the carrier density enhanced near the surface. 19 In relation to the EELS measurements, the surface excitations in the absence and the presence of a surface spacecharge layer have been calculated by means of a hydrodynamic theory combined with a step density-profile model, 19,28,29 a semiclassical local-response theory formulated in Ref.…”