Experimental Study On Optical Properties Of Near Infrared Optoelectronic Materials And Devices

The research work in this paper is mainly based on the infrared spectral characterization method including the steady-state absorption spectroscopy,transmission spectroscopy,photoluminescence(PL)spectroscopy,electroluminescence(EL)spectroscopy,time-resolved photoluminescence(TR-PL)spectroscopy and photocurrent(PC)spectroscopy.This paper focuses on the study of defect states and near infrared optical properties of glass based Pb Se quantum dots(Pb Se:Glass),the erbium doped silicon(Si:Er),and the copper zinc tin sulfide(CZTS).The main contents and results are as follows:(1)Pb Se:Glass is an ideal near-infrared quantum light source material because of its large exciton Bohr radius,strong quantum confinement effect,mature preparation method and high fluorescence quantum yield.However,the highly degenerate exciton ground state,the high Auger recombination rate and the low volume fraction of quantum dots have direct influence on the optical gain of the Pb Se:Glass,and its application as the near infrared laser source.In the research of Pb Se:Glass,the optical properties of Pb Se:Glass with diameter of 3.4 nm were systematically studied.The carrier dynamics under different excitation conditions were revealed.The potential applications of Pb Se:Glass as laser gain medium was analyzed.The main innovative results are as follows:i)The processes of amplified spontaneous emission(ASE)from two excited states with energies of 1.13 e V and 1.32 e V of Pb Se:Glass with the same thresholds of 20?J·cm^-2 were observed simultaneously.The multi-level luminescence model and carrier transfer dynamics of Pb Se:Glass under different excitation conditions(e.g.continuous laser excitation,low-power and high-power pulsed laser excitation)were established.ii)The limitations of Pb Se:Glass as potential optically pumped laser material are revealed.Compared with the glass based Pb S quantum dots,The higher threshold of ASE and the lack of stimulated emission from the ground state indicate that the application potential of Pb Se:Glass as optical pumping laser material is relatively weak.(2)For the Si:Er system,when the 4f electron of Er³⁺transit from the first excited state ⁴I_13/2 to the ground state ⁴I_15/2,the emission wavelength is 1.54?m,which just falls on the lowest absorption window of quartz fiber.So it is considered as one of the best candidates for silicon-based light source.However,due to the low solid solubility of erbium in silicon,serious temperature quenching effect and small absorption cross section,the quantum efficiency of Er doped silicon is far below the requirements of application.In the research of Si:Er,the luminescent properties of two samples with different annealing conditions(e.g.deep cooling and traditional RTA annealing)and two devices with different structure(e.g.plane type and vertical type)were studied.The main interim results are as follows:i)Compared with traditional RTA,the‘deep cooling'technology can effectively reduce the PL quenching effect of erbium-doped silicon material by two orders of magnitude.The internal quantum efficiency of the samples treated by‘deep cooling'technology,which is two orders of magnitude higher than the previous record.These improvements are mainly benefit from‘deep cooling'technology,which can effectively avoid the occurrence of Er related donor impurity clusters.ii)Both the EL spectra of the vertical and planar LED devices treated by‘deep cooling'technology show the near-infrared emission of 1536 nm.Under different conditions of current injection,the high-efficiency luminescence of vertical erbium-doped silicon LED at 1536 nm mainly comes from the spontaneous emission of erbium ion;while the planar erbium-doped silicon LED can achieve stimulated emission(amplified spontaneous emission)at 1536 nm with a threshold of 6 m A(0.8 A/cm²).These results demonstrate that erbium-doped planar LED device treated by‘deep cooling'technology is expected to achieve silicon based laser at communication band.iii)The carrier relaxation dynamics in Er doped silicon treated by‘deep cooling'technology was revealed by TR-PL spectra.The reason for the excitation wavelength selectivity in the photoluminescence spectra measurement of Si:Er was explained.The new luminescence mechanism of Si:Er,which is different from the existing research consensus,was revealed.(3)CZTS is considered to be an ideal photovoltaic cell material because of abundant element reserves,non-toxic,high absorption coefficient and optimal band gap.However,the efficiency of CZTS thin film solar cells is far from practical application due to the existence of abundant defects.In the research of CZTS,a variety of optical characterization including transmission spectra,reflection spectra,photoluminescence spectra and photocurrent spectra of Sn-rich CZTS thin film solar cells revealed the existence of band tail state and deep level defects.Based on the theoretical calculation and experimental results,the origin of band tail and deep-donor states are clarified.The main results are as follows:i)We confirm that the band-tail states in CZTS originate from the high concentration of 2Cu _Zn+Sn _Zn defect clusters,whereas the deep-donor states originate from the high concentration of Sn _Zn.ii)The optical characterization of Sn-poor CZTS highlight that a Sn-poor composition is critical for the reduction of band-tailing effects and deep-donor defects and thus the overcoming of the severe open-circuit voltage deficiency problem in CZTS solar cells.