The Optical And Spin Polarization Properties Of GaAs(Sb,Bi)

As the unceasing breakthrough of the semiconductor technology, traditional transistor based on the migration of the electrons is approaching it’s physical limit. Traditional transistors operated based on the migration of the electrons. On the one hand, it is quite energy consuming. On the other hand, the operation speed is limited by the electron mobility. Spin is another important characteristic. The energy consumption of spin-flip is far below and the speed of spin-flip is much faster than electron migration. So the quantum computers and quantum memories based on spintronics are with great advantages.For the development of applicable spintronics devices, three fundamental problems need to be solved, those are spin generation, spin transportation and spin detection. As there are multiple mechanisms of spin relaxation, to clarify the interaction between electrons and various potentials in materials is so important. Through this, we can optimize the materials purposefully to make spintronics devices practical.Recent years, researchers found that incorporate N into Ga As would enable spin dependent recombination at room-temperature. This effect makes the spin polarization of Ga As N much higher than that of Ga As. Sb, Bi and N are all V element, which implies incorporate Sb and Bi into Ga As may also result some novel spin properties. Thus, research the spin characteristic of Ga As Sb and Ga As Bi is very valuable for future spintronics devices.The bandgap of ternary alloy Ga As Sb is tunable between 1.42 e V(870nm) and 0.726 e V(1700nm) by selecting the specific composition of Arsenic and Antimony. Since the working wavelength is highly tunable especially covered 1310 nm and 1550 nm, which are very important wavelengths for optical communication, makes Ga As Sb highly applicable for potential use. So far, photoelectric devices such as infrared light emitting diode, infrared laser, infrared photodetector, terahertz quantum cascade laser, terahertz heterojunction bipolar transistor based on Ga As Sb had all been developed. But the research which focus on the spin properties of Ga As Sb is rarely seen.Bismuth is the heaviest element without radioactivity. Introduce it into Ga As will result giant spin orbit splitting. The splitting energy was calculated to be 2.15 e V(But have never been successfully grown yet). Since Bi and As have large difference in size and electronegativity, incorporate Bi into Ga As would lead anticrossing interaction between localized Bi states and the valence band of Ga As. This interaction leads the valence band split to two subbands, makes giant bandgap reduction. Previous experiment found that the bandgap of Ga As would reduce about 90 me V for 1% of Bi incorporation and the bandgap of Ga As would reduce to 0.8e V(1550nm) for 10% of Bi incorporation. This means Bi is an efficient controller of bandgap. Typical infrared optoelectronic devices such as infrared laser diode, infrared photodetector, solar cell have all been developed base on Ga As Bi. But as the large difference of size and electronegativity between Bi and As, the growth of Ga As Bi is very hard, which made the research based on Ga As Bi is quite insufficient.Based on the vast application prospect and the entire research status, we carried out our researches. The main work content as follow.1. We use continuous wave optical orientation spectra and Hanle effect to investigate the optical spin polarization and effective spin dephasing time as functions of temperature. We got a optical polarization of about 21% around 120 K, and the effective spin lifetime declined from 1.5ns to 20 ps as the temperature rose from 5K to 200 K. Our research revealed that a little composition of Sb incorporation would lead strong spin-orbit interaction, and thus modified the spin property of Ga As. Moreover, we had also analyzed the recombination time and spin relaxation time with varied temperature, and identified the spin mechanism of Ga As Sb.2. Based on the main factors of which influenced the polarization most, we applied a longitudinal magnetic field and a post growth thermal annealing process to our Ga As Sb samples. Both processes enhanced the spin polarization degree obviously. Through applying a 10 T magnetic field, the polarization of photoluminescence doubled from 19% to 40% at 105 K. On the other hand, through post growth thermal annealing process, which can shortened the electron lifetime, the polarization of photoluminescence quadrupled from 6% to 23%. We illustrated the principle of these two method which can enhance the polarization of photoluminescence in detail.3. Continuous wave photoluminescence(CWPL) and time resolved photoluminescence(TRPL) were used to investigate the optical properties of Ga As Sb at varied temperature. We found two photoluminescence signals in our sample, and both of them blue-shifted as the incident density increase. This revealed both signals came from the localization state. The TRPL showed the photoluminescence was not monotonous decline after the laser pulse. We proposed a semi quantitative model to explain this strange finding, and analyzed the extracted parameters one by one.4. The Ga As Bi film grown by molecular beam epitaxy was investigated by photoreflectance technique. Through the photoreflectance spectra, we found abnormal broadening and intensity variation. The line shape of E0 transition and E0+ΔSO transition both broadened as the Bi composition got higher, and the broadening of E0 transition was more drastic. We consider the broadening of E0 transition mainly come from the light hole and heavy hole splitting caused by the alloy uniformity, meanwhile, the band tail state resulted from Bi pair and other Bi related defects also prompt the broadening of photoreflectance spectra. Besides, as the Bi composition got higher, the ratio of modulation signal of E0 transition to E0+ΔSO transition downwarded from 35 to 4, Which means the incorporation of Bi would modify the optical activity of light hole band, heavy hole band and spin orbit splitting band together, but the degree of impact is quite different. Through the measurement and analysis of the photoreflectance excitation spectra, we confirmed that the incorporation of Bi could modulate the photoelectric device properties of the origin materials very efficiently.5. We investigated the intensity relation between Ga Bi mode and Ga As-LO mode in Ga As Bi. Though referring former work which was based on Ga As N, we proposed a method to identify the Bi composition in Ga As Bi by extract and compare the intensities of Raman scattering. Our method showed a good agreement with the composition determined by peak shift for Bi composition lower than 3%. Thus, our method provides a alternative way to identify Bi composition in Ga As Bi with diluted Bi incorporation.