Heterojunctions Including Narrow Bandgap Semiconductor Bismuth Telluride Thin Films

As a device that can directly convert thermal energy into electrical energy,thermophotovoltaic cells have attracted much attention in recent years.So far,most of the researches about the thermophotovoltaic cells focus on those which work well under the high temperature(above 1000 K)radiation(wavelength is smaller than 3.5?m).There are few reports about the cells which can absorb the infrared photons radiated from low temperature(below 500 K)heat sources.In fact,because the low temperature radiation exists more widely than the high temperature one,the thermophotovoltaic cells working under the low temperature radiation have more extensive applications.As the temperature of the heat source decreases,the energy of the radiated photons becomes smaller,so such low-temperature thermophotovoltaic cells should be made of semiconductor materials with a narrower band gap.In this thesis,the electrical and optical properties of the heterojunctions including narrow-bandgap semiconductor Bi₂Te₃(0.15-0.17 eV)thin films were studied.And the feasibility of applying the heterojunctions to low-temperature thermophotovoltaic cells was analyzed.For the requirements of thermophotovoltaic cells operating at room temperature,a model of co-diffusion of carriers in Bi₂Te₃/Sb₂Te₃ heterojunctions was proposed.The Bi₂Te₃/Sb₂Te₃heterojunction was prepared,and the effect of temperature on the I-V characteristics of the heterojunction was investigated.In order to meet the testing needs of thermophotovoltaic cells,an infrared spectrum response test system was designed in the experiment.It is demonstrated that the absorption cut-off wavelength of Bi₂Te₃/Sb₂Te₃ thermophotovoltaic cells is as high as8.2?m.Bi₂Te₃/Si thermophotovoltaic cells were fabricated by substituting the p-type Sb₂Te₃thin films with p-type single crystalline Si wafers.By optimizing the band structure of the heterojunction,the output performance of the cells under low-temperature radiation was improved.It is also demonstrated that the resistivity of Si and the thickness of Bi₂Te₃ thin films have important effects on Bi₂Te₃/Si thermophotovoltaic cells.