An extremely high room temperature mobility of two-dimensional holes in a strained Ge quantum well heterostructure grown by reduced pressure chemical vapor deposition

Abstract

An extremely high room temperature two-dimensional hole gas (2DHG) drift mobility of 4230 cm 2 V %1 s %1 in a compressively strained Ge quantum well (QW) heterostructure grown by an industrial type RP-CVD technique on a Si(001) substrate is reported. The low-temperature Hall mobility and carrier density of this structure, measured at 333 mK, are 777000 cm 2 V %1 s %1 and 1.9 ' 10 11 cm %2 , respectively. These hole mobilities are the highest not only among the group-IV Si based semiconductors, but also among p-type III-V and II-VI ones. The obtained room temperature mobility is substantially higher than those reported so far for the Ge QW heterostructures and reveals a huge potential for further application of strained Ge QW in a wide variety of electronic and spintronic devices.

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

“…Recently, epitaxially grown layers of Ge grown on SiGe on a standard Si(001) substrate have been shown to have extremely high room temperature hole mobility of up to 4500 cm 2 /Vs due to formation of a two dimensional hole gas (2DHG). 2,3 Compressive strain of the Ge epilayer induced by epitaxial growth results in 2DHG formation and the holes have enhanced mobility due to their lower effective mass and reduced scattering factors. Low temperature 2DHG mobility in excess of 1.3 Â 10 6 cm 2 /Vs has been achieved.…”

“…A detailed study of the material properties of this heterostructure has been published elsewhere. 3 Magnetotransport, Hall effect, and resistivity measurements were performed using a Hall bar geometry produced using photo-lithography. Thermally evaporated Al was used as a contact material, post-annealed to form a contact with the QW.…”

Strained germanium for applications in spintronics

“…Strain in a Ge epilayer or QW can be tuned by growth onto a silicon germanium (SiGe) relaxed buffer layer, the magnitude of the strain is tuned through the Ge composition of the buffer. Strain changes the mobility of carriers in Ge, with the highest mobilities to date found in Ge layers grown on an $70-80% Ge SiGe buffer layer [16][17][18]. Ge is highly compatible with conventional Si-based technology, and can be grown with high material and electrical quality onto standard orientation silicon substrates.…”

Spin-splitting in p-type Ge devices

“…This procedure produces high mobility p-Ge QWs with ambient temperature values $4500 cm 2 /V s, an order of magnitude larger than p-type doped Si. 14,15 The mobility is determined by background acceptor impurity scattering although interfaces and point defects can also limit the mobility; this is discussed in Section III B. The high quality growth process has been outlined in a series of publications over the last few years.…”