| Mercury cadmium telluride (Hg1-xCdxTe, MCT) is a very important semiconductor material of infrared (IR) detector and infrared thermal imaging. Compared to other materials, it has many advantages. It can be seen as a pseudo binary compound, (HgTe)1-x(CdTe)x, with an arbitrary proportion. It has a variable band gap changing from -0.3 to 1.6 eV, depending on the parameter x, which includes almost the entire IR band. Its optical absorption coefficient is large. The internal quantum efficiency of the IR detector made by the HgCdTe is almost 100%. The mobility of the electrons and the holes is very high. The intrinsic recombination mechanism causes the carriers to have a long carrier lifetime and a low thermal production rate. The devices can work at a low temperature. The lattice match between the HgCdTe and the CdTe/HgTe is well, which is helpful to prepare a high quality hetero-epitaxy structure film. The residual impurity concentration can be low 1014 cm-3. The p-type and n-type semiconductors can be obtained easily by doping. In a long time, the preparation and wide application of the HgCdTe single crystal thin film has many disadvantages, such as low deposition rate, high cost, strict experimental requirements. All of these restrict the growth of the multilayer and complex thin films and the require of the high quality devices.This paper preliminary studies the feasibility of the growth of the HgCdTe thin films by pulsed laser deposition (PLD) methods. The HgCdTe is an IR material which has a high absorption efficiency of the IR laser. The YAG laser is a near- infrared laser source with high beam quality, narrow pulse width, well stability and large power. The YAG laser source is used to ablated the high purity compound target which is the same as the film. It can strength the compatibility between the PLD and the semiconductor technology, and solve the difficulty of the practicality of HgCdTe thin film by PLD. In this research, we study the influence of the experimental parameter of the pulsed laser deposition (PLD) on the growth of the HgCdTe thin film, and the results of the experiment have been analyzed and explained. The finite difference method and the Monte Carlo method were used to simulate and analyzed the experimental results. The main contents include:1. The PLD being used to grow the HgCdTe thin film has many advantages, such as easy control, low growth temperature and the high film quality. We analyzed the principle of the PLD technique at first, and the effect of laser energy density (E), substrate temperature (Ts), gas pressure (P) and the distance between the target and the substrate (Dt-s) on the growth of the thin films were studied.2. In the experiment, the HgCdTe thin film was grown on the different substrates. The different lattice mismatch, thermal expansion rate and thermal conductivity between the film and the substrate will affect the quality of the expitial thin film. The Al2O3(0001), GaAs(100) and Si(111) were chosen as the substrate materials. The results of the experiment indicated that the different lattice structure between the film and the substrate would cause a large distortion area at the interface between the film and the substrate. The large thermal expansion mismatch will lead to a large stress in the film. The film will crack, exfoliate or wrinkle. The substrate materials with a large thermal conductivity cause the adatoms to have a large mobility on the substrate surface. According to the analysis of the experiment results, the HgCdTe thin film grown on the Al2O3 substrates have a high crystalline and surface quality. The composition of the film is close to that of the target. The quality of the HgCdTe film deposited on the GaAs and Si substrates is bad.3. The change of the distance between the target and the substrate leads to the change of the kinetic energy and spatial distribution of the incident atoms arriving at the substrate surface. The crystalline quality, elemental composition and surface morphology of the HgCdTe thin films are in relation to the change of the substrate position. Choosing an appropriate distance between the target and the substrate is very important to obtain a high quality thin film. The SiTe4 with a zinc blende Body-Centered Cubic (bcc) structure can be formed between the HgCdTe film and the Si substrate at a close position. The problem of the lattice mismatch and the difference of the thermal expansion coefficient between the Si substrate and the HgCdTe thin film may be solved by the formation of the Si-Te compound.4. The kinetic energy and mobility of the adatoms can be affected by the substrate temperature. The structure and the crystalline quality of the HgCdTe thin films improve when the deposition temperature increases from 100 to 200℃. At 200℃, the thin films have a smoothest surface and a monocrystalline structure with a predominant crystalline orientation (111). When the substrate temperature is over 250℃, the HgCdTe thin films will be thermodynamically unstable and Cd-rich.5. When the ablation particles in the plasma fly from the target to the substrate, their internal energy and average kinetic energy will be affected by the ambient gas pressure. The growth rate, composition and structure of the film will be affected by the chang of the kinetic energy and the surface mobility of the adatoms with the different gas pressures. The thin films deposited at a range of pressure from 5×10-1 to 5×10-3 Pa have a high quality. In our experimental conditions, the HgCdTe thin film deposited at 5×10-2 Pa has the highest crystal quality, but the composition of Hg in the film is the lowest.6. The influences of incident laser energy on the kinetic energy and density of the particles in the plasma were studied. An appropriate laser energy leads the incident atoms to have a high surface mobility and the quality of the film can be improved. The laser energy has an important effect on the crystalline quality, surface morphology, composition and resistivity of the HgCdTe thin films by PLD. The HgCdTe thin film deposited by PLD at 150 mJ laser energy has the highest crystalline quality, smoothest surface, highest resistivity and the composition of the film are the closest to that of the target. When the incident laser energy is over 200 mJ, the incident atoms have a too high kinetic energy. The HgCdTe thin films deposited at these conditions will be unstable, and the quality of the films is poor.7. The dynamic model and the basic equation of the isothermal expansion and the adiabatic expansion of the PLD are set up. The finite difference method was used to simulate the evolution of the plasma produced by the laser ablating the target with the time. The evolution rule of the three main atoms in the HgCdTe plasma (Hg, Cd and Te) was obtained. According to the experimental parameters, we obtain the spatial distribution of the film thickness and the distribution characteristics of the film composition.8. The Monte Carlo method was used to simulate and analyze the initial stage surface morphology of HgCdTe thin film by PLD at the different temperatures. The simulation results show that the number of the islands and particles increases obviously with the increase of the substrate temperature. The surface morphology of the film changes from disorder to order gradually. When the temperature is too high, the link presents between the islands. The islands on the film surface are consecutive. But the too high temperature will lead the sputtering rate of the adatoms to increase, and cause the quality of the film to decrease.This paper includes four parts. The first chapter briefly introduced the properties and the recent research progress of the HgCdTe material. In the second chapter, the principle of PLD and the effect of the experimental parameters on the growth of the thin films were studied. The main experimental instruments and the test means were studied in this parts. From the third to the seventh chapter, the HgCdTe thin films are the main research object. We discuss the crystalline quality, surface, composition and other properties of the HgCdTe thin films in the different conditions (substrate materials, distance between the target and the substrate, substrate temperature, gas pressure and incident laser energy). The results of the experiment were analyzed. The finite difference simulation of the plasma and the Monte Carlo method of the initial stage surface morphology of the PLD HgCdTe film were researched in the eighth chapter.
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