Study On Optical Properties Of Doped Multiple Quantum Wells

Currently, there is much interesting in the so called ’terahertz (THz) gap’ of frequencies that lie between traditional electronic and optical technologies. The corresponding frequency (or wavelength) range of THz radiation is0.1-10THz (3000-30imμm). Due to the potential applications that THz based devices have, a plenty of research have been done concerning about issues such as how to produce a THz radiation. Thus, low-dimensional semiconductor nanostructures, particularly quantum well systems, are often introduced in the manufacture of THz-based sensors and detectors. As technologies toward THz light-emitting detectors and emitters would require engineering of the energy levels to favor radiative emission, the doped QWs can meet this requirement. In this thesis, the optical properties of a series of beryllium (Be) δ-doped multiple GaAs/AIAs quantum wells have been investigated by photoluminescence (PL), Raman and Fourier transform infrared absorption spectroscopy in low temperatures. Combined with related theory, the internal transitions of Be acceptors have been clearly observed and simulated.First, the development process, research significance of THz technology, along with the research background of THz radiation have been described; Then, the preparation process of samples used in this article has been illustrated; Followed by a simple description of structures of a quantum well and the impurities within it; Next, the thesis elaborates the experimental results obtained from PL, Raman and Fourier transform infrared absorption spectroscopy of all samples; After that, theories and formulas used here to calculate atomic energy levels are listed; At last, a comparison has been made between the experimental data and theoretical results.In the PL spectra, transitions between free excitons, acceptor bound excitons and free to bound excitons have been observed. The energy splitting of Be acceptor ground state (1S3/2) to excited state (2S3/2), as well as the dependence of such splitting on quantum wells width have been obtained.From Raman scatting experiment, longitudinal vibration mode (LO) in GaAs wells, as well as surface vibration mode (IF) lies in the interface of GaAs and AlAs, have been clearly seen. More importantly, the transitions related to Be acceptor ground state (1S3/2) to excited state (2S3/2) have been observed. The results of Raman experiments are consistent with photoluminescence measurements.In Fourier transform infrared absorption spectra, three major interband transition absorption lines can be seen, which derived from the Be acceptor ground state to three odd-parity excited states.The results can be served as a complement to Raman data.The energy splitting of Be acceptor ground state (1S3/2) to excited state (2S3/2) is calculated by an iterative shooting algorithm underthe single-band effective mass and envelop function approximations. The results show that the transition energy of1S3/2â†'2S3/2is increased with the decrease of quantum wells width, and this trend is in agreement with the data obtained in experiments.