Group III-V Diluted Magnetic Semiconductor Materials and Related Methods of Formation (22025)
The present invention provides a growth technique to achieve epitaxial, single-phase films of III-V diluted magnetic semiconductors (DMSs) with large Mn concentrations that exhibit ferromagnetic order at room temperature. The III-V DMS compositions and/or methods of this invention are suitable for device applications and utility in the fabrication of non-volatile magnetic random access memories (MRAM) integrated with semiconductor circuitry; spin-polarized transport devices such as read heads in magnetic disc recorders, and in magnetic field sensors.
ADVANTAGES: The growth technique overcomes limitations of the prior art. This method affords high throughput sample growth, versatility, and uniform large area deposition. Reduced manufacturing costs are anticipated by avoiding ultra-high vacuum processes.
SUMMARY: Group III-V diluted magnetic semiconductors (DMSs) have received considerable attention due to their observed ferromagnetism and have been proposed as an approach to spin-sensitive electronics, and the possibility of fabricating all semiconductor devices which employ magnetic semiconductors as the active layers. Ferromagnetism is achieved when sufficient manganese (Mn) concentrations are incorporated into the III-V semiconductor host, yet low enough to prevent undesirable phase separation. Mn doping performed using molecular beam epitaxy (MBE), has achieved ferromagnetic transition temperatures of -238°C for In1-xMnxAs and -163°C for Ga1-xMnxAs single-phase films. However, for widespread application, the ferromagnetism should be stable at room temperature (27°C). MBE thin film deposition is also inherently slow and requires the generation and maintenance of ultra-high vacuum (UHV) conditions.
This invention employs metal organic vapor phase epitaxy (MOVPE) to achieve epitaxial, single-phase films of III-V DMSs with large Mn concentrations that exhibit ferromagnetic order at or above room temperature. The process affords heteroepitaxial growth of III-V DMS films such as In1-xMnxAs with x > 0.1 on substrates such as GaAs (001).
Thus, single-phase ferromagnetic In1-xMnxAs films on GaAs (001) with x = 0.14 have been prepared using MOVPE techniques at growth temperatures as high as 520°C. An x = 0.1 sample, exhibited a saturation magnetization of 62 emu/cm3 with a remanence of 10 emu/cm3 and a coercive field of 400 Oe, by SQUID magnetometry at -268°C. This saturation magnetization exceeds the 50 emu/cm3 measured for MBE fabricated In 0.8Mn 0.2As grown at 300°C. When the temperature was increased to 27°C, the MOVPE sample's saturation magnetization decreased only to 49 emu/cm3, whereas that of the MBE sample became negligible. (J. Vac. Sci. Technol. B 20, 1582, 2002)
Bruce Wessels and Aaron Blattner
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