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...

We have developed a very controllable fabrication process of an extremely narrow (∼10 nm) quantum wire metal-oxide-semiconductor field-effect transistor (MOSFET) on a separation-by-implanted-oxygen (SIMOX) substrate using anisotropic etching and selective oxidation technique. The drain current versus gate voltage characteristics show oscillations caused by Coulomb blockade even at room temperature. The oscillations split into several sharp peaks when the temperature is decreased, indicating that the channel is separated by several serial coupled quantum dots and that the quantum levels of these dots correspond to the observed fine peaks.

We present a new electro-chemical method for incorporating high concentration Er ions deep into porous silicon layers and its intense photoluminescence at ∼1.54 μm at room temperature. Porous silicon layers prepared by anodic etching of p-type silicon substrates in HF/H2O are immersed in ErCl3/ethanol solution. Then the negative bias relative to a counter platinum electrode is applied to the samples. Er3+ ions are drawn into fine pores of the porous silicon layers by the electric field. After thermal annealing at ∼1300 °C in an O2/Ar atmosphere, the samples show sharp and intense Er3+-related photoluminescence at ∼1.54 μm at room temperature upon excitation with an Ar ion laser.