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Experimental Studies Of Electron Spin Dynamics In Semiconductors Using A Novel Radio Frequency Detection Technique

Electronic Theses of Indian Institute of Science

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Title Experimental Studies Of Electron Spin Dynamics In Semiconductors Using A Novel Radio Frequency Detection Technique
 
Creator Guite, Chinkhanlun
 
Subject Electron Spin Dynamics
Semiconductors - Electron Spin
Optical Spin Orientation
Spin Polarization
Radio Frequency Modulation
Radio Frequency Detection
Electro-optic Cell
Electron Spins
Electronic Spin Detection
Electronic Spins
Spin Hall Effect
Radio Frequency Coil
Spin Polarized Electrons
Electrodynamics
 
Description A novel experimental setup has been realized to measure weak magnetic moments which can be modulated at radio frequencies (~1–5 MHz). Using an optimized radio-frequency (RF) pickup coil and lock-in amplifier, an experimental sensitivity of 10 -15 Am2 corresponding to 10 -18 emu has been demonstrated with a one second time constant. The detection limit at room temperature is 9.3 10 -16 Am2/√Hz limited by Johnson noise of the coil. In order to demonstrate the sensitivity of this technique it was used to electrically detect the polarized spins in semiconductors in zero applied magnetic fields. For example in GaAs, the magnetic moment due to a small number (~ 7 x 108) of spin polarized electrons generated by polarization modulated optical radiation was detected.
Spin polarization was generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by the sensitive radio-frequency coil. Using a radio-frequency lock-in amplifier, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of ~ 10–20% could be determined for Ge at 1342 nm excitation wavelength at 127 K. In the presence of a small external magnetic field, the signal decayed according to the Hanle Effect, from which a spin lifetime of 4.6 ± 1.0 ns for electrons in bulk Ge at 127 K was extracted. The spin dynamics in n-Ge was further explored and the temperature dependence of the spin lifetime was plotted for a temperature range of about 90 K to 180 K. The temperature dependence of the optical pumping efficiency was also measured though no quantitative conclusions could be derived.
The signals observed for semi-insulating GaAs, n-GaAs, GaSb and CdTe which are direct gap semiconductors are much larger than expected (almost two orders of magnitude). An attempt was made to explain this unexpected behavior of these direct gap semiconductors using the spin hall effect.
 
Contributor Venkataraman, V
 
Date 2015-08-05T11:41:02Z
2015-08-05T11:41:02Z
2015-08-05
2012-06
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/handle/2005/2458
http://etd.ncsi.iisc.ernet.in/abstracts/3173/G25475-Abs.pdf
 
Language en_US
 
Relation G25475