Valence Band Offset at Amorphous Boron Carbide / Silicon Interfaces
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Valence Band Offset at Amorphous Boron Carbide / Silicon Interfaces Sean W. King1, Marc French1, Milt Jaehnig1, and Markus Kuhn1 1
Logic Technology Development, Intel Corporation, Hillsboro, OR 97124, U.S.A.
ABSTRACT In order to understand the fundamental charge transport in a-B4-5C:H/Si heterostructure devices, we have utilized x-ray photoelectron spectroscopy to determine the valence band offset at interfaces formed by Plasma Enhanced Chemical Vapor Deposition of a-B4-5C:H on (100) Si. For such interfaces, we observed relatively small valence band offset values of ± 0.25 eV. INTRODUCTION Due to extreme thermal-mechanical properties [1-3], low atomic number (Z), high neutron capture cross section [4], negative electron affinity [5], and low dielectric constant (k) [6], boron and boron compound materials are of interest for numerous applications including neutron detectors [3,7], diffusion barriers [8], protective optical coatings [9], field emission devices [8,10], and low-k interlayer dielectrics [6]. In many of these applications, charge transport across the interface between the boron compound and another material is an important factor in the success of the device. As one example, B and BX (X = C, N, P, As) neutron detectors rely on the ionization produced by neutron-induced reaction products. These energetic ions can interact within the BX active layer to produce electrons, which in turn lose their energy through the production of electron-hole pairs that may be swept across a pn heterojunction interface with Si [4,11]. A determining factor for the charge transport across this interface is the valence and conduction band alignment between the boron compound and Si [12]. However, the actual band alignment at B/Si and BX/Si interfaces have received relatively little attention [13,14]. In this regard, we have utilized x-ray photoelectron spectroscopy (XPS) to determine the valence band offset for a-B4-5C:H/(100) Si interfaces. We show that the valence band offset for the a-B45C:H/Si interface is relatively small at 0.2±0.2 eV. EXPERIMENT The boron carbide films were deposited on 4” square Si (100) double side polished substrates cleaved from larger 300 mm diameter wafers. The a-B5C:H thin films were deposited at temperatures on the order of 350 °C by plasma enhanced chemical vapor deposition (PECVD) using a mixture of argon and orthocarborane (o-B10C2H12) [11,15,16]. The a-B4C:H films were deposited at temperatures on the order of 350 °C via sputter deposition using a poly-crystalline B4C target and an Ar working gas [17]. Prior to deposition, the Si substrates were given a clean in dilute HF to remove the native surface oxide and produce a hydrogen terminated surface. Table 1 summarizes some of the key material properties for the a-B4-5C:H compounds investigated in this study including Rutherford backscattering (RBS) and nuclear reaction analysis (NRA) atomic composition, RBS B/C ratio, x-ray reflectivity mass density, nanoindentation Young’s Modulus and hardness, and resistivity. Additional details concerning
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