Growth And Characterization Of Hg_1-xMn_xTe Diluted Magnetic Semicoductor

Hg_1-xMn_xTe is a ternary diluted magnetic semiconductor formed by substituting Hg²⁺ with magnetic ions Mn²⁺ in HgTe lattice. In the absence of magnetic field, the band structure and other semiconductor properties of Hg_1-xMn_xTe are very similar to those of its sister compound Hg_1-xCd_xTe, but possess some superiority over Hg_1-xCd_xTe in some aspects. Therefore, Hg_1-xMn_xTe becomes a perspective substitute for Hg_1-xCd_xTe as detector material. In addition, Hg_1-xMn_xTe possesses a number of attractive properties which are displayed in magnetic field due to the existence of magnetic ion Mn²⁺.Preparation of high quality Hg_1-xMn_xTe crystal is of vital importance to the development of the material and the relative device. In order to reduce dislocations and Hg vacancies in the as-grown crystals, a series of improvement methods has been adopted, such as to improve the coating technologies of carbon film on the inner wall of quartz ampoule, to improve the distribution of thermal field in the furnace during Hg_1-xMn_xTe crystal growth, to prolong anneal time of the as-grown ingots after crystals grown, to adjust the raw materials composition and to change the working procedure of vacuum encapsulation etc.. By combining the above techniques, several Hg_1-xMn_xTe ingots with the dimensions ofΦ15×135mm² were grown. The perfect surface of the as-grown ingots proves the high quality of the carbon film coated on the inner surface of the crucible. The modified techniques have also markedly decreased the defect density, and therefore upgraded the properties of Hg_1-xMn_xTe crystals. The carrier density, Hall mobility and resistivity of the wafers obtained from the ingot grown by the modified techniques are about 1.5×l0¹⁶cm^-3, 500cm²Â·V^-1·s^-1 and 0.75Ω·cm, respectively. The properties of as-grown crystal have exceeded the requirement of the device fabrication, where the carrier density should be lower than 3.0×10¹⁶cm^-3, and the mobility should be higher than 400cm²Â·V^-1·s^-1.The electronic properties of several Hg_1-xMn_xTe wafers were characterized by Van Der Pauw method at 77K and room temperature respectively. Results show that the conductivity of a part of Hg_1-xMn_xTe wafers change from p type at 77K to n type at room temperature. The high ratio of electron to hole drift mobility and narrow forbidden band of Hg_1-xMn_xTe should play key roles in determining the conductivity type of the semiconductor. The results also indicate that Van Der Pauw method is only suit to test the resistivity of Hg_1-xMn_xTe wafers at room temperature, but not for other electronic parameters. In addition, the electronic properties of several Hg_1-xMn_xTe wafers before and after chemical polish were characterized by Van Der Pauw method at 77K. Results show that the resistivity and Hall coefficient of the wafers are increased after etching, while Hall mobility and carrier density are decreased. The maximum of resistivity decreases by 25 percent, and the maximum of Hall mobility increases by 31 percent, but Hall coefficient and carrier density change only by about 2 percent. The high density dislocations in un-etched surface layer are responsible for the decrease of Hall mobility. However the Hall mobility before chemical polish is 21 percent higher than that after etching treatment. It is an abnormal phenomenon. All the experimental results are explained using a three layer model.According to the requirements of device fabrication, ohmic or Schottky metal contacts should be prepared on the semiconductor surface.â… -â…¤behaviors of Au/Hg_1-xMn_xTe and Al/Hg_1-xMn_xTe contacts were measured by Aligent4155câ… -â…¤tester. The results show that Au/Hg_1-xMn_xTe is an ohmic contact, while Al/Hg_1-xMn_xTe is Schottky contact with the barrier height of 0.38eV.The experimental results of microhardness tested on Hg_1-xMn_xTe surface show that there exists a surface damaged layer on Hg_1-xMn_xTe wafer surface after cutting and polishing, which softens the surface, indicated by the low surface hardness. A Te enrichment layer with highen hardness will be formed on the wafer surfaces after etched with Br-MeOH solution. The hardness measured on Hg_1-xMn_xTe surface after 3 minute etching is very close to that of a perfect Hg_1-xMn_xTe surface. The microhardness of Hg_1-xMn_xTe decreases with the increase of the applied load, which shows a typical indentation size effect (ISE). The variation of hardness under different applied load can be normalized by Hays-Kendall theory and PSR model. The microhardness of Hg_1-xMn_xTe increases markeOdly with x value. When x value increases from 0 to 0.26,the hardness of Hg_1-xMn_xTe increases from 26 kgf·mm^-2 to 50 kgf·mm^-2.Magnetization measurements show that Hg_0.89Mn_0.11Te crystal possesses paramagnetic properties in temperature range from 5K to 300K. The magnetic susceptibilities of Hg_0.89Mn_0.11Te obey Curie-Weiss laws at the temperature above 40K. There exists a weak antiferromagnetic interaction between Mn²⁺. While the susceptibility curves go down in the lower temperature range below 40 K and the paramagnetism of the crystal enhances. The resistivity of Hg_0.89Mn_0.11Te under the magnetic field is dependent on Hall electrical field and the sp-d exchange interaction. Hall electrical field contributes a positive component for the resistivity, while sp-d exchange interaction contributes a negative term. Hall electrical field plays major role in the high temperature range. However, with the decrease of temperature, the effect of sp-d exchange interaction on the resistivity exceeds gradually that of Hall electrical field, and becomes the dominate effect in the range of 5 K to 30 K, which leads to the dramatic decrease of resistivity. The difference of the resistivities at 5 K between the measurement result without magnetic field and that at 6.5 Tesla is as high as three orders.