Strained Quantum Wells for P-channel InGaAs CMOS
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1108-A12-01
Strained Quantum Wells for p-Channel InGaAs CMOS Padmaja Nagaiah, Vadim Tokranov, Michael Yakimov, and Serge Oktyabrsky College of Nanoscale Science and Engineering, University at Albany, SUNY, 255 Fuller Road, Albany, NY 12203 ABSTRACT We present experimental results on the effect of strain on hole transport in InGaAs quantum well (QW) structures. Indium content was varied from lattice matched to high compressive stress in InGaAs/InP QW and the transport properties were analyzed at various temperatures (T = 77-300 K) using Hall measurements. The effect of QW thickness (4-20 nm) on hole transport is also presented. The current best results include room temperature mobility and sheet resistance of 390 cm2/V-s and 8500 Ω/sq., respectively. It was observed that the mobility had a T-1.8 dependence indicating similar scattering mechanism in almost all of the samples with prominent mechanism being due to interface and barrier scattering. Further optimization of p-channel for InGaAs CMOS needs to be performed using the above results as guidelines. INTRODUCTION III-V materials are being investigated as potential replacement for silicon CMOS technology due to their superior electron transport properties. However, CMOS circuits require both high performance n-channel and p-channel devices. Since the effective mass of holes is an order of magnitude higher than that of electrons1, the hole mobility is much less than electron mobility negating the possible advantages of III-V CMOS circuits. To overcome this fundamental difficulty, structures incorporating biaxial compressive strain were proposed2. Numerous works on valence band structure modification in strained quantum wells have been published3-4. Compressive strain in the QW splits the valence sub-bands into heavy hole (HH) band and light hole (LH) bands. This splitting of bands reduces the in-plane effective mass of band in the lowest HH band compared to the bulk, whereas the normal component of the effective mass is higher. This is supposed to lead to high hole mobility in the plane and better confinement of the carriers in the QW. However, just a few experimental studies are reported for room temperature hole transport in strained InGaAs QWs5, 7. Biaxial strain in these heterostructures are usually obtained by increasing of indium content “x” in the ternary InxGa1-xAs QW. In this paper, we evaluate the hole transport properties in strained QWs using Hall-effect measurements. THEORY Figure 1 shows the calculated valence band energy barrier variation due to splitting of HH and LH bands in strained bulk InxGa1-xAs grown on InP substrate as the indium content is varied. For indium composition less than 53% (x=0.53 is the lattice matched composition), the strain induced is tensile and the valence band splits such that the Light Hole (LH) band is higher than the Heavy Hole (HH) band. Alternatively, for x > 0.53, the QW is compressively strained in the growth plane and the valence band splits with the HH band higher than the LH band. The valence band barrier is highe
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