UCLA

Electrical detection of spin transport in a semiconductor (SC) channel is one of the key requirements to realize spintronics devices. Among various SC materials, the high-mobility two-dimensional electron gas (2DEG) confined in a modulation doped quantum well structure (MODQW) is of particular interest for device applications. This is because the high mobility promises for a long spin diffusion length of coherent transport as well as large spin signal for easy sensing. Meanwhile, the effective spin manipulation is achievable either by enhanced Rashba spin-orbit interaction from an asymmetric E-field structure, or by direct control of discrete density of states (DOS) within the quantum well structure. Despite of these merits, very few studies of direct electrical spin injection into 2DEG have been reported so far, mainly because of the difficulty in making reliable ferromagnetic (FM) contacts to the buried 2DEG channel. In literature, only a few reports in Si/SiO2 and III-V matrices are available up to now; however, electrical detection of spin transport in the high-mobility 2DEG in a Si/SiGe MODQW has not been reported. To make continuous progress of Si-based spintronics and to take full advantage of current CMOS technology, there is an urgent need to develop Si-based spintronics devices.

In this thesis we present two related projects: first is spin injection in Ge; second is spin injection in Si two-dimensional electron gas (2DEG) system. It is the knowledge built up from the Ge project helps us successfully demonstrate electrical spin injection in Si 2DEG in a Si/SiGe MODQW using FM Mn-germanosilicide (Mn(Si0.7Ge0.3)x) end contacts, which is a new approach to circumvent the difficulty of etching process adopted for the typical spin valve devices. The experiments show that the spin-polarized electrons could be laterally injected into one side of the 2DEG confined at the Si/SiGe interface, and subsequently detected from the other side by the magnetoresistance (MR) of a FM/2DEG/FM spin valve. Most important of all, symmetric resistance steps were clearly observed from a series of FM/2DEG/FM spin valve devices with different channel lengths (Lch = 1.5~3.5 μm), by which the spin diffusion length and spin lifetime are calculated to be 4.5 um and 16 ns at 1.9 K, respectively.