Conservation of the Lateral Electron Momentum at a Metal-Semiconductor Interface Studied by Ballistic Electron Emission Microscopy

Abstract

We report on ballistic electron emission microscopy and spectroscopy studies on epitaxial (3-5 nm thick) Bi(111) films, grown on n-type Si substrates. The effective barrier heights of the Schottky barrier observed are 0.58 eV for the Bi=Sið100Þ-ð2 Â 1Þ and 0.68 eV for the Bi=Sið111Þ-ð7 Â 7Þ. At the step edges of the epitaxial films a strong increase of the ballistic electron emission microscopy current is observed for Bi=Sið111Þ-ð7 Â 7Þ, while no increase occurs for Bi=Sið100Þ-ð2 Â 1Þ. These observations can be explained by the conservation of the lateral momentum of the electron at the metal-semiconductor interface. DOI: 10.1103/PhysRevLett.102.136807 PACS numbers: 73.23.Ad, 73.20.At, 73.30.+y, 73.40.Àc Since the invention of ballistic electron emission microscopy (BEEM) by Bell and Kaiser two decades ago [1,2], studies on the conservation of lateral electron momentum at the interface formed between metals and semiconductors have remained puzzling. Schowalter and Lee [3,4] studied ballistic electron emission spectroscopy (BEES) for Au films grown on Si substrates with different crystallographic orientations. Assuming that the lateral electron momentum at the metal-semiconductor interface is conserved [2] the BEEM currents were expected to differ dramatically due to different projections of the conduction band minima of the Si on the (111) and (100) plane. However, almost identical BEEM currents were measured. These results were later confirmed by Weilmeier et al. [5,6]. In the case of Pd on Si, Ludeke and Bauer [7] attributed the observed equality of transmission across (111) and (100) to interface scattering randomizing the electron momentum. As discussed by García-Vidal et al.[8] and Bell [9], the results found on Au samples may be explained without additional electronic scattering processes, because the electronic band structure of the transition metals (Au, Ag, Pd, etc.) exhibits a band gap in the [111] direction, requiring a minimal lateral component of the electronic momentum. Taking into account the matching conditions at the metal-semiconductor interface, they predicted a similar onset for the BEEM current, but a higher intensity for Au=Sið111Þ in agreement with the experiments.A different situation is found with CoSi 2 =Sið100Þ versus CoSi 2 =Sið111Þ. The band structure of CoSi 2 allows the propagation of electrons at k k ¼ 0, and due to the excellent quality of the epitaxial layers there is very little diffuse scattering of electrons. The latter is confirmed by the high resolution of detail at the metal-semiconductor interface obtained by BEEM imaging [10], indicating that the electrons are limited to a very small cone within the CoSi 2 . A theoretical description by García-Vidal et al. [8,[11][12][13][14] could explain the high spatial resolution for BEEM and has predicted that the onset for the BEEM current should be shifted for the (111) versus the (100) substrate, due to the conservation of the lateral momentum at the interface. However, the experimental results for the BEEM current are contra...

Schottky barrier height measurements of Cu/Si(001), Ag/Si(001), and Au/Si(001) interfaces utilizing ballistic electron emission microscopy and ballistic hole emission microscopy

“…The SBHs for many metal/semiconductor systems have been extensively studied using BEEM and BHEM. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] With BEEM the tip can be positioned with a Electronic address: vlabella@albany.edu nanoscale resolution giving spatially resolved spectra and barrier heights, which has been performed for Au/GaAs(001) diodes where a Gaussian distribution of barrier heights was observed in support of interface dipole models. 27 The power law form of the Bell and Kaiser model is the standard method for extracting the Schottky barrier height from the BEEM spectra.…”

Nanoscale mapping of the W/Si(001) Schottky barrier

“…16 BEEM and BHEM have been used to measure the Schottky barrier height of many different metals to semiconductor interfaces. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] BEEM and BHEM are three terminal scanning tunneling microscopy (STM) techniques; hot electrons (BEEM) or holes (BHEM) are injected into a grounded metal film and travel ballistically towards the interface. Electrons (or holes) which have enough forward momentum after traveling through the metal to surmount the Schottky barrier pass into the semiconductor and are collected as the BEEM (or BHEM) current.…”

Hot electron attenuation of direct and scattered carriers across an epitaxial Schottky interface

“…This mode of BEEM has been successfully applied to study transport across various M/S interfaces and probing the spatial homogeneity of transport across such interfaces [1,6,[14][15][16][17]. BEEM can also be operated in a reverse mode, known as the reverse BEEM (R-BEEM), that is realized by applying a positive tip bias [12] as shown in Fig.…”