Investigation On Surface Treatments And Contact Resistivity Of CdMnTe Crystal

In recent years, the ternary compound semiconductor Cd Mn Te has got extensive attentions and researches. The Cd Mn Te crystal is regarded as one of the most ideal room temperature X-ray and γ-ray detector material, due to its excellent photoelectric properties. Great improvements have been achieved on the crystal growth of high-quality Cd Mn Te crystals, but to fabricate high-performance Cd Mn Te detectors, a great work is still required on the device fabrication technology including the metal/Cd Mn Te contacts and surface treatments. In this thesis, the Cd Mn Te wafers were prepared by various surface treatments, such as, Mechanical Polishing(MP), Chemical Polishing(CP), Chemical-Mechanical Polishing(CMP) and Chemical Mechanical Polishing followed Chemical Polishing(CMP+CP). The Au/Cd Mn Te contacts were prepared using vacuum evaporation deposition and Au Cl3 electroless method on the treated Cd Mn Te surfaces. The Monocycle Transmission Line Model(MTLM) was used to get the specific contact resistivity(ρ) of Au/Cd Mn Te contacts after various surface treatments and annealing. The main results were as follows:(1) By the Atomic Force Microscopy(AFM) measurement, the surface roughness values of the Cd Mn Te wafers treated by MP, CP, CMP and CMP+CP were 8.2 nm, 5.1 nm, 1.4 nm and 0.84 nm, respectively. The X-ray photoelectron spectroscopy(XPS) measurement shown that the atomic percentage of(Te+Te4+)/(Cd+Mn) from the MP, CP, CMP and CMP+CP surface were 1.07, 2.00, 1.40 and 1.10, respectively. The Cd Mn Te surfaces after the MP and CMP+CP treatments were close to stoichiometric composition, while the CP and CMP treated surfaces were enriched with Te. Therefore, the CMP+CP treatment was an ideal surface treatment for Cd Mn Te wafers, and the ultra-smooth surface with stoichiometric composition was achieved.(2) After surface treatments, the vacuum evaporation method and Au Cl3 electroless method were adopted to prepare Au/Cd Mn Te contact. The current-voltage(I-V) measurement was conducted. It was found that the Au/Cd Mn Te contact on the CP treated surface by the vacuum evaporation method was Schottky contact with a barrier hight of 0.826±0.005 e V. The Au/Cd Mn Te contacts prepared by Au Cl3 electroless method were ohmic contacts. The I-V curves shown that the ohmic coefficients of Au/Cd Mn Te contacts were 0.81, 0.95 and 0.98 for CP, CMP and CMP+CP treated surfaces, respectively. Obviously, the I-V measurement cannot meet the requirements of accurate measurement.(3) The MTLM method was adopted to calculate the contact resistivity(?) of Au/Cd Mn Te prepared by Au Cl3 electroless method. The influence of surface treatments and annealing on the contact resistance of Au/Cd Mn Te was discussed. The MTLM contacts on Cd Mn Te were prepared by photolithography. The ? value of Au/Cd Mn Te treated by CP, CMP and CMP+CP were 544.5 Ω·cm2, 89.0 Ω·cm2 and 15.0 Ω·cm2, respectively. After the annealing treatment, the ? values further decreased to 313.6Ω·cm2, 30.2Ω·cm2 and 3.9Ω·cm2, respectively. It’s found that the high quality ohmic contact could be achieved by improving the surface treatment and annealing process of Au/Cd Mn Te contact.