Weak antilocalization of high mobility holes in a strained Germanium quantum well heterostructure

Abstract

We present the observation of weak antilocalization due to the Rashba spin-orbit interaction, through magnetoresistance measurements performed at low temperatures and low magnetic fields on a high mobility (777,000 cm(2) V(-1) s(-1)) p-Ge/SiGe quantum well heterostructure. The measured magnetoresistance over a temperature range of 0.44 to 11.2 K shows an apparent transition from weak localization to weak antilocalization. The temperature dependence of the zero field conductance correction is indicative of weak localization using the simplest model, despite the clear existence of weak antilocalization. The Rashba interaction present in this material, and the absence of the un-tuneable Dresselhaus interaction, indicates that Ge quantum well heterostructures are highly suitable for semiconductor spintronic applications, particularly the proposed spin field effect transistor.

Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

“…11 Prior to the recent report of hole mobility in excess of 1 Â 10 6 cm 2 /Vs at a carrier density of 2.9 Â 10 11 cm À2 in a Ge QW, 1 the record value of mobility was 120 000 cm 2 /Vs with a carrier density of 8.5 Â 10 11 cm À2 . 12 The study of quantum transport in high mobility Ge 2DHGs since this discovery has primarily focussed on the spin-orbit interaction in heterostructures of this type [13][14][15] and on the composite fermions and the fractional quantum Hall effect in high magnetic fields. [4][5][6] Here, we study low temperature quantum transport in a Ge QW heterostructure, modulation doped with 2 Â 10 18 cm À3 of boron (B) and a delta layer of B.…”

Strained germanium for applications in spintronics

“…Figure 7 shows schematics of typical Ge QW heterostructures exhibiting the Rashba S-O interaction. The following is a summary of the key recent findings in this area, focusing on detection and quantification using three methods: analysis of 'beating' patterns in Shubnikov-de Haas (SdH) oscillations [57,59], analysis of weak antilocalisation (WAL) [56,59,60] and cyclotron resonance using terahertz excitation [61]. One of the key advances necessary to observe the Rashba S-O interaction using SdH oscillations is the significant enhancement of 2D hole mobility at low temperatures.…”

“…To date, measurement of WAL has been used in two Ge QW systems, grown by different techniques, to quantify the cubic Rashba interaction [56,60]. Firstly, Moriya et al studied a Ge QW grown by SS-MBE on a Si 0.5 Ge 0.5 buffer, resulting in a high degree of biaxial compressive strain (2.1%), and with a low heavy hole mobility in the 2DHG (5000 cm 2 V À1 s À1 ) at low temperatures [56].…”

“…The interaction could be enhanced/suppressed by applying a bias electric field using an electrostatic gate. A more complex system was studied by Foronda et al, with a high low temperature mobility 2DHG (780000 cm 2 V À1 s À1 ) in a Ge QW with a modulation delta dopant layer of boron in proximity [60]. The structures were grown by RP-CVD.…”

Hole weak anti-localization in a strained-Ge surface quantum well

“…Further details of materials growth and characterization are described elsewhere [17]. The same epitaxial growth technology resulted in the creation of strained Ge QW heterostructures with superior low-and room-temperature electronic properties [18][19][20] enabling the observation of various quantum phenomena including the fractional quantum Hall effect [21], mesoscopic effects due to spin-orbit interaction [2,[22][23][24][25] and terahertz quantum Hall effect [26].The studied devices have a Hall-bar geometry defined by a top-gate electrode operated in accumulation mode ( Fig. 1.b).…”