Research Of Surface Properties And Micro-nano Structures Of Antimonide Materials

In recent years, due to the unique properties of antimonide lasers, such as high output power, high reliability, small volume, high efficiency and simple modulation, antimonide semiconductor materials have been considered as the first choice to fabricate the 2-5μm semiconductor lasers. Wavelength expansion and wavelength locking have long been the main topics in the development of semiconductor lasers, and distributed feedback semiconductor laser diode(DFB LD) with built-in Bragg grating, the key element for wavelength-locked semiconductor lasers, has received widespread attention, and the demands for the DFB LD have been expanding. But the serious surface problems of antimonide materials restrict the development of the devices, which lead to the catastrophic optical damage(COD) and seriously limit the development of antimonide LDs, especially for the output power and the reliability of LDs.Therefore, in this dissertation, we have studied the origin and containing of surface state problems of the antimonide semiconductor materials, and mainly studied various ways of passiviation in order to improve the light emitting efficiency and the reliability of the antimonide semiconductor lasers; The design and preparation of Bragg grating structure satisfies the requirement of mid-IR distributed feedback antimonide semiconductor lasers. The performance of material surface microstructure was studied by combining near-field optical and far-field optical surface microanalysis technologies such as surface morphology analysis. The main research contents and research results are as follows.(1) Theoretical study on the surface properties and micro-nano structure of antimonide materials.We analyzed the origin of the antimonide material surface states, and discussed the effect of surface states on the degradation of semiconductor laser. The results indicated that the non-radiative recombination caused by surface states was the main factor to cause catastrophic optical damage and limit laser property enhancement. Then, the basic processes and effective methods of passivation were described in detail. Finally, the important influence of built-in Bragg grating for DFB-LD was studied. These provided a theoretical foundation and reference for the design and preparation of material surface with a good performance.(2) The research on preparation techniques and characterization of grating micro-nano structure of antimonide materials and characterization analysis techniques.Firstly, wet and dry passivation technology methods were proposed to solve the problem of high surface state density of GaAs, GaSb, GaAsSb. Secondly, the preparation technique of the DFB-LD with built-in Bragg grating was described. Finally, we elaborated the principle and analysis method of the photoluminescence(PL), near-field scanning optical microscopy(NSOM/SNOM), atomic force microscopy(AFM), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS).(3) The research of sulfur wet passivation technology for antimonide materials.Four passivation methods have been proposed: 1) Ammonium sulfide((NH4)2S) neutral solution; 2) Electrochemical etching combined with(NH4)2S neutral solution; 3) S2Cl2 solution; 4) Depostion ZnS layer through two-step solution, used as passivation solution to passivate the GaAs, GaSb, GaAsSb surface. Using the PL, AFM, SEM, XPS to study the surface properties of passivatied GaAs, GaSb, GaAsSb. Research results indicated that the PL intensity of GaAs, GaSb, GaAsSb after passivation increased(3~5)×,(14~25)×,(24~25)×, respecpectly. The PL intensity was further improved compared with that of general sulfur wet passivated method.(4) The research of nitrogen passivation technology for antimonide materials.In order to solve the secondary oxidation problem of the wet passivation of sulfur solution, and the other inevitable disadvantages, such as side product, rough surface and so on, a dry passivation was proposed, based on nitrogen plasma enhanced atomic layer deposition(PEALD). In the PEALD system, the NH3 plasma is firstly used to etch the suface of the materials, then AlN film deposition to the surface was performed. Using PL, AFM, SEM, XPS to study the surface properties of nitrogen passivatied GaAs, GaSb, Ga AsSb. Research results indicated that nitrogen passivation based PEALD technique can control the surface state effectively. GaAs, GaSb, GaAsSb treated under the optimum condition of plasma power 200 W, plasma etching 400 cycles, AlN thin film deposition temperature of 250 oC and AlN films deposited 200 cycles gave the best passivation effect, and the Ga-O, As-O and Sb-O bonds on the material surface have been removed completely, and PL intensity of passivated GaAs, GaSb, GaAsSb increase roughly 2.5×, 15×, 14×, respectively; The PL intensity decreased only 20% after 15 days storage, it then remain unchanged, the passivation effect would remain long-time effective.(5) The research of built-in Bragg grating micro-nano structure based on antimonide materials.In this dissertation, 4.1μm DFB LD was theoretically analysed, the order number, period, duty cycle and depth of built-in Bragg grating were optimized, and the Bragg grating of 4.1μm DFB LD was prepared with electron beam direct writing(EBDW) exposure method and the inductively coupled plasma(ICP) etching. The optimized Bragg grating with order number of 2, period of 1μm, the duty cycle of 0.25, and depth of 30 nm on GaSb substrate, moreover, the optimized Bragg grating with order number of 2, period of 1.1μm, the duty cycle of 0.25, and depth of 30 nm on GaAsSb substrate. In order to solve the problem that ICP etching depth was sensitively affected by the surface states of GaSb and GaAsSb, we put forward a method using nitrogen passivation to prepare the gating. The fabricated Bragg grating was characterized by near-filed optical technique and microscopic characteristics technique. The results show that the optimal solution of the GaSb with combination of the nitrogen passivation technique can solve the problem. SNOM, SEM, AFM were used to study the grating micro-nano structure. Research results indicated that the ICP etching rate is not affected after the pretreatment of nitrogen passivation, and the etching depth can be controlled accurately. The grating satisfies the design requirement, with good characteristics such as surface morphology.