Elsevier

Microelectronics Journal

Volume 39, Issue 8, August 2008, Pages 1080-1082
Microelectronics Journal

Characteristics of β-SiC/Si heterojunction with a SiGe buffer film

https://doi.org/10.1016/j.mejo.2008.01.044Get rights and content

Abstract

In the present work, preparation of SiGe thin buffer film was performed on p-Si single crystals, non-doped β-SiC epitaxial layer was grown on SiGe/Si substrate by means of lower pressure chemical vapor deposition (LPCVD) and ohmic contacts were formed to fabricate typical multilayer sandwich structure of Al/β-SiC/SiGe/P-Si/Al heterojunction. Contrasted β-SiC/SiGe/P-Si heterojunction with β-SiC/P-Si, scanning electron microscope (SEM) images, reverse breakdown voltage, IV and CV characteristics are studied. Theory and experimental results show that introduction of SiGe buffer layer can improve interface properties of heterojunction, reverse breakdown voltage and rectification ratio (RR) of the heterojunction.

Introduction

A lot of research work has been carried out on heterojunctions in recent years, because of their applications in microelectronics and optoelectronics [1], [2], [3], [4]. One of the most interesting heterojunctions is the SiC/Si heterojunction, which exhibits very interesting properties as a Schottky diode [5], a high speed switch, [6] a solar cell [7], [8], etc.

The reverse breakdown voltage and rectification ratio (RR) are important quality parameters of heterojunctions. Because of comparatively large mismatching degree (20%) of lattice constant between SiC layer and Si substrate, the reverse breakdown voltage of SiC/Si heterojunction is low, so more and more attention was paid to study in improving breakdown voltage and RR of SiC/Si heterojunctions. The present work is a contribution to this direction.

In the present work, Thin buffer layer of SiGe was prepared on p-Si single crystals, non-doped β-SiC epitaxial layer was grown on SiGe/Si substrate by means of lower pressure chemical vapor deposition (LPCVD) and ohmic contacts were formed to fabricate typical multilayer sandwich structure of Al/β-SiC/SiGe/P-Si/Al heterojunction. Contrasted β-SiC/SiGe/P-Si heterojunction with β-SiC/P-Si, scanning electron microscope (SEM) images, reverse breakdown voltage, current–voltage (IV) and capacitance–voltage (CV) characteristics were studied. SEM images indicate that introduction of SiGe buffer layer improves interface properties of heterojunction, so reverse breakdown voltage of β-SiC/SiGe/P-Si heterojunction is improved from 100 V to 140 V, CV and IV measurement results show that SiGe buffer layer reduces built-in voltage of the heterojunction and improves RR of the heterojunction at 1 V by over one order of magnitude.

Section snippets

Experiments

p-Type single-crystal Si wafers (ρ=10–12 Ω cm) with cutting of 〈1 0 0〉 are selected as substrates, after rinsed with tetra-ethylene, acetone, ethanol without water and deionized water in turn, substrates were boiled in boiling mixed liquid of NH4OH–H2O2–H2O (1:1:3) for 10 min, etched with HF (10%) to remove surface oxidizing layer, rinsed with deionized water, boiling mixed liquid was substituted with HCl–H2O2–H2O (3:1:1) and same disposal processes are repeated.

Preparation of SiGe thin buffer layer

Results and discussion

In order to study interface characterization of β-SiC/SiGe/P-Si heterojunction structure, before Ohmic contacts were formed, part of samples were sawed in the direction of [0 1 1] and sectional scanning was performed using SEM technology. Fig. 2 shows the scanning images of β-SiC/SiGe/P-Si and β-SiC/P-Si heterojunctions, respectively. From Fig. 2(b), it can be clearly observed that SiGe buffer layer exists and the interface is neat, there is no obvious holes or cracks both on the side of the Si

Conclusions

SiGe thin buffer layer was prepared on p-Si single crystals by means of LPCVD, β-SiC epitaxial layer was grown on SiGe/Si substrate to fabricate β-SiC/SiGe/P-Si heterojunction. In this heterojunction, the measured resistivity of SiGe/Si substrate is 8–10 Ω cm, the carrier concentration is 5×1015 cm−3, the electron concentrations of β-SiC (1×1018 cm−3) is far larger than that of SiGe/Si substrate. From theory of one-sided abrupt junction [9], the depletion layer mainly exists on the side of SiGe/Si

References (11)

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  • Impact of a SiGe interfacial layer on the growth of a SiC layer on Si with voids at the interface

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    Improvements of crystal quality and lowering of growth temperatures have also been observed when adding Ge-containing precursors during SiC film growth [10, 11], and strain engineering, using Ge in the substrate [12], in a buffer layer [13], or even in an over-layer [14], has led to improved quality of SiC films. The use of Ge prior to SiC film growth has furthermore been reported to improve the electrical properties of the SiC/Si heterointerface [15, 16]. Along the same lines of thought, an AlN buffer layer has been demonstrated as an efficient diffusion barrier for Si, leading to improved surface morphology of the grown SiC film [17], and a BP buffer layer has been shown to decrease the density of crystal defects due to an improved lattice matching with the grown SiC film [18].

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    The explicit dependence of the voltage factor on temperature demonstrates the tunneling mechanism not being the predominant instrument in the considered devices. Such a trend of A = f(T) concurs with that concluded for other different devices; these include: a-Si:H/p-Si [14,15,21], a-Si1 − xCx:H/c-Si [22,23], a-SiC/p-Si [24,25] as well as p-GaAs/n-Si [26]. Meanwhile, other works show constancy for the function A = f(T), as in the case of ZnO/CdTe [27].

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