Effect of Electron Scattering on Second Derivative Ballistic Electron Emission Spectroscopy inAu/GaAs/AlGaAsHeterostructures

Abstract

We present a quantitative study of the second voltage derivative (SD) of ballistic electron emission spectra of Au͞GaAs͞AlGaAs heterostructures to probe the effect of electron scattering on these spectra. Our analysis of the SD spectra shows that strong electron scattering occurs at the nonepitaxial Au͞GaAs interface, leading to an experimentally observed redistribution of current among the electron transport channels. We also show that the effects of hot-electron scattering inside the semiconductor modify the spectra and are sensitive to the heterojunction band structure, its geometry, and temperature. [S0031-9007(99)09041-9] PACS numbers: 72.10.Fk, 73.20.At, 73.40.Kp, 73.50.Gr Ballistic electron emission microscopy (BEEM), a three-terminal modification of scanning tunneling microscopy, has recently been shown to be a powerful tool for nanometer-scale characterization of the spatial and electronic properties of semiconductor structures. Since the pioneering work of Kaiser and Bell [1], the capability of BEEM to probe the electronic properties of semiconductors on the local scale has been demonstrated for several systems, including Schottky contacts [2-4] and buried heterojunctions [5][6][7].The shape of the BEEM spectrum in the threshold region has to be known in order to derive the correct Schottky or heterojunction barrier energies. Several theoretical models were developed to describe the experimental BEEM spectra. Two commonly used models, based on a planar tunneling formalism [8] and on the transverse momentum conservation at the metal-semiconductor (m-s) interface, are the Bell-Kaiser (BK) model [9] and the Ludeke-Prietsch (LP) model [10]. The LP model extends the original BK theory to include the energydependent electron mean free path (mfp) in the metal base layer and the quantum mechanical transmission at the m-s interface. Experimentally distinguishing between the BK and LP models is still difficult, because the quantitative difference between them is comparable with the experimental error, and both of them can fit experimental data reasonably well [6,11,12]. Recently, BEEM theory was extended to the case of buried heterostructures [13], where transmission at the heterojunction interfaces in addition to the m-s interface was considered.The assumption of transverse momentum conservation, made in the above models, is questionable for the case of nonepitaxial m-s interfaces, which are not atomically abrupt. A deviation from the ballistic picture was experimentally observed, e.g., for Au͞Si [14], Pd͞Si [15], and Au͞GaAs [1,6]. To consider electron scattering at the m-s interface, the m-s interface-induced scattering (MSIS) model was proposed in Ref. [16]. In the strong scattering limit, this model was found to describe the absolute magnitude of the experimentally observed BEEM current for Au͞GaAs and Au͞Si systems. However, since the observed BEEM spectra are a superposition of current contributions from several different transport channels, it is difficult to conclusively extract the different conducti...

Bandgap and band offsets determination of semiconductor heterostructures using three-terminal ballistic carrier spectroscopy

“…Although scattering rates may be further surpressed at 4.2 K, the contribution of X electrons is still largely attentuated since their mfp is still much shorter than the combined thickness of the GaAs cap and the barrier layers (∼50 nm). Previous BEEM work on direct-gap GaAs/Al x Ga 1−x As (x≤0.42) SB HJs found that the collector current is composed only of Γ and L electrons [16], and the contribution from the offaxis L channel is greater due to interfacial scatterings at the m-s interface. The main results from the quaternary AlGaInP alloy system are shown in Fig.…”

Ballistic hot-electron transport in nanoscale semiconductor heterostructures: Exact self-energy of a three-dimensional periodic tight-binding Hamiltonian

“…A heterostructure can be placed in the base itself 7 or in the collector, 8 close to the base-collector interface. Much work in this field has focused on ballistic transport through single barriers, 9 double resonant barriers, 10 quantum dots, 11 and superlattices. [12][13][14] A well-developed theory has been implemented to predict the observed voltage-current relation to the actual transmission function through the structure by making use of the bulk conduction-band offsets and effective masses.…”

Enhanced solid-state thermionic emission in nonplanar heterostructures

“…7 The nonepitaxial interface scattering and lateral momentum nonconservation have been verified by ballistic electron emission microscopy for some metal/semiconductor interfaces. 8,9 However, the thermionic emission current enhancement needs to be further quantified for these experiments.…”