Masao Sakuraba

A Study on B Atomic Layer Formation for B-Doped Si1-xGex(100) Epitaxial Growth Using Ultraclean LPCVD System

Atomically controlled doping in heterostructure is a key technology to fabricate high-performance ultrasmall semiconductor devices. Atomic-layer doping of B and P in Si1-xGex epitaxial growth has been reported [1]. In the previous works, atomic layer formation of B on Si(100) and subsequent epitaxial growth of Si were investigated [2]. Recently, because the decomposition of BCl3 is rather gentle compared with B2H6, BCl3 is paid attention as a doping gas. In the present work, self-limited B atomic layer formation on Si1-xGex(100)(x=0-1) using BCl3 gas in an ultraclean low pressure CVD (LPCVD) was investigated. Si1-xGex epitaxial growth on Si(100) was performed at 450-500 C in a SiH4-GeH4 gas mixture using an ultraclean LPCVD reactor (Fig. 1), e.g. the strained 23 nm-thick Si0.7Ge0.3 film and the strain-free 200 nm-thick Ge film were prepared [3]. Formation of a B atomic layer on the substrates was performed by introduction of a BCl3-He-H2 or BCl3-He-Ar gas mixture. BCl3 exposure temperature dependence of B atom amount on Si1-xGex/Si(100) is shown in Fig. 2. It is found that B atom amount tends to increase with increasing

Room-Temperature Resonant Tunneling Diode with High-Ge-Fraction Strained Si1-xGex and Nanometer-Order Ultrathin Si

For the purpose of heterointegration of Si-based group IV semiconductor quantum effect devices into Si large-scale integrated circuit, formation of atomically flat heterointerfaces in quantum heterostructure by lowering Si barrier growth temperature was investigated in order to improve negative differential conductance (NDC) characteristics of high-Gefraction strained Si1-xGex/Si hole resonant tunneling diode. It was found that roughness generation at heterointerfaces is drastically suppressed by utilizing, Si barriers with nanometer order thickness deposited using Si2H6 reaction at a lower temperature of 400 o C instead of SiH4 reaction at 500 o C after the Si0.42Ge0.58 growth. NDC characteristics show that difference between peak and valley currents is effectively enhanced at 11-295K by using Si2H6 at 400 o C, compared with that using SiH4 at 500 o C. Thermionic-emission dominant characteristics at higher temperatures above 100 K indicates a possibility that introduction of larger barrier height (i.e., larger band discontinuity) enhances the NDC at room temperature by suppression of thermionic-emission current.

Effect of Si/Si1-yCy/Si Barriers on the Characteristics of Si1-xGex/Si Resonant Tunneling Structures

P-type double barrier resonant tunneling diodes (RTD) with the single Si0.6Ge0.4 quantum well and double Si0.6Ge0.4 spacer have been realized by using an ultra clean low-pressure chemical vapor deposition system. The effect of Si1-yCy layer on the characteristics of the devices was shown by comparing the current-voltage (I-V) characteristics of RTDs of the barriers of Si layers with that of Si/Si1-yCy/Si structures. The peak voltage was gradually increased and the resonant current decreased obviously with increasing C content in the Si/Si1-yCy/Si barriers. The origin of the phenomena above can be attributed to the C related deep acceptor levels in the Si/Si1-yCy/Si barriers. The possible mechanism for the observed I-V characteristics was shown more clearly by increasing C content to 3% and changing the thicknesses of Si and Si1-yCy layers in the Si/Si1-yCy/Si barriers.

Atomically Controlled Formation of Strained Si1-xGex/Si Quantum Heterostructure for Room-Temperature Resonant Tunneling Diode

High-quality quantum heterostructure of group IV semiconductors such as nanometerorder thick strained Si1-xGex/Si has enabled room-temperature resonant tunneling diode (RTD) [1], and it is important for integration of specified applications, e.g. high frequency oscillation or high speed switching into Si LSIs. In order to improve the RTD performance at room temperature, not only by high quality of heterostructure [2], increase of Ge fraction (i.e. strain and band discontinuity) in the heterostructure is one of the effective ways. In this work, p-type RTD with Si/strained Si1-xGex/Si(100) heterostructure has been investigated [1-4], and it has been demonstrated that introduction of high-Ge-fraction ultrathin Si1-xGex layers with atomic-order flat heterointerfaces is effective to improve negative differential conductance (NDC) characteristics at room temperature (Fig. 1). Additionally, hole tunneling properties through nanometer order thick Si barriers have been also investigated to explore possibility to overcome limitations of the present materials and structures. B-doped and undoped strained Si1-xGex/Si heterostructures were epitaxially grown on Si(100) in a SiH4 (or Si2H6)-GeH4-(B2H6)-H2 gas mixture using an ultraclean hot-wall low-pressure CVD system [5]. Because total Si1-xGex thickness is estimated to be within critical thickness, crystallinity degradation can be avoided. This is essential for uniformity and reproducibility in manufacturing. Especially to suppress the roughness generation at heterointerfaces for higher Ge fraction, Si barriers were deposited at a lower temperature of 400 C with Si2H6 (instead of conventional SiH4) after the Si0.42Ge0.58 growth. By this deposition condition, the roughness generation at heterointerfaces (as well as surface) can be effectively suppressed compared with the case of SiH4 reaction at 500 C [1].

Atomic-Order Thermal Nitridation of Si1-xGex(100) at Low Temperatures by NH3

Atomic-order control of interface structure between the gate insulator (SiO2 or high-k materials) and Si1-xGex is indispensable for high-performance Si1-xGex channel MOS devices. In the previous work, in order to realize atomic-layer (AL) nitridation, we have reported atomicorder thermal nitridation process of Si(100) at low temperatures [1]. In the present work, thermal nitridation of Si1-xGex(100) (x=0-1) using NH3 gas in an ultraclean low pressure CVD (LPCVD) was investigated.