The Convergence Characteristic Of The Forward I-V Characteristic Curves Of Emitter-base Junction Of Bipolar Junction Transistor

Connect the base and collector of transistor, then put it in a constant temperature oven. Different values of V_BE corresponding to the different I_BE are measured after the temperature to be stabilized. The current values of 1mA, 2mA, 5mA, 10mA, 20mA were taken, and measurement was performed once per 30℃from 25℃to 145℃. The data we obtained was called the base data. Measuring the base data of different transistors and analyzing them, we can find that the characteristic curves measured with the voltage as the abscissa and the natural logarithm of the current as the ordinate and junction temperature as the parameter are beelines between 25℃to 145℃. If we extend the curves corresponding to the different temperature, these curves will almost converge at a point in the first quadrant. We can see that the points of intersection corresponding to the different curves are not lapped well but dispersed. Because the difference of the abscissa of every two convergent points is relatively small, we can consider that they converge at one point, and the average of the abscissa of all convergent points is the abscissa of the holistic convergent point. There are similar converge characteristic for log(I_F) versus V_BE curves.The voltage corresponding with the convergent point V_F equals to the summation of the valueof the bandgap F_g0 and nKT₁γ/q , and the latter in proportion to V_F is very small. The difference of V_F of different transistors is because of the difference of band gap caused by the difference of the doping concentration. We performed some similar measurements for a Schottky diode, and the result proved that there are similar converge characteristic. Theoretical analysis and experimental results proved that the physical meaning of the convergent point is same with the transistor. The convergent characteristic and physical meaning of the convergent point can be extended from p-n junction to metal-semiconductor contact and heterojunction, from Si, Ge to new type semiconductor materials such as GaAs, InP and GaN, from bipolar transistor to Schottky diode, MESFET and ultraviolet light-emitting diode. The temperature is higher, the change of input current I_F according to the same change in value of the base-emitter voltage V_BE is smaller. We can get the relation between slope of ln(I_F) versus V_BE curves and temperature from both calculational and regression way, and results from two ways are same.The convergent characteristic of base data can be used to study the electrical character of transistor. First we get the relation between slope and temperature from regression way, and get the slope of beeline according to any temperature, then get the coordinate of convergent point. In this way, we not only know the slope of the beeline, but also know that this beeline comes by the convergent point, so the I-V characteristic curve corresponding to any temperature can be drawn. Analyze the infrared images of transistors and band together the thermal spectrum and base data, then we can get the I- V characteristic curves of transistor when it was shot to get infrared images. Deal with the base data and we can get the relation between slope of ln(I_F) versus V_BE curves and temperature from regression way. Change the ordinate of the I-V characteristic curves of transistor when it was shot to get infrared images to the natural logarithm of the current, so the curve is nearly a beeline. Get the slope of the beeline and then we can get the junction temperature from the relation between slope of ln(I_F) versus V_BE curves and temperature.