Current Transport Mechanism Of 4H-SiC Schottky Barrier Diode

Silicon carbide(SiC)is one of the key materials of the third generation semiconductors.Its excellent physical properties make it apply in the field of high temperature,high frequency and large power.SiC Schottky diode has many advantages such as high breakdown voltage,low on-resistance,rapid switching speed and high temperature resistance.It has broad application prospects in many fields,such as national economy and military affairs.Power electronics is one of the most representative engineering applications.In this thesis,low doped 4H-SiC epitaxial wafer was used to fabricate SiC Schottky diode.Photolithography process was used to pattern electrodes,and Schottky contact layer Ni/Au was deposited on the Si(0001)face of the wafer by magnetron sputtering.The Ni metal layer was deposited on the back of highly-doped substrate and treated by high temperature rapid annealing to form Ohmic contact.Following the above steps,4H-SiC Schottky barrier diode(SBD)are fabricated.The effect of HF treatment on 4H-SiC SBD was investigated.The current transport mechanism was analyzed by combined current method,which was used to extract parameters of SBD.Untreated SiC SBD has high ideality factor(n=1.52)and low Schottky barrier height(SBH=1.28 eV).After treated by HF,the ideality factor was decreased to 1.008 and the Schottky barrier height was increased to 1.73 eV.HF surface treatment can effectively remove the thin oxide layer of Si face which is formed during the alloying process.HF treatment improves the performance of 4H-SiC SBD.If SiC SBD is not an ideal diode,its ideality factor will deviate from 1 and the Schottky barrier height extracted by traditional thermionic emission theory will not be accurate.Thermionic field emission(TFE)current induced by the surface states in non-ideal diode is the main factor to deviate from the ideality through the combined current method.It also concludes that the actual Schottky barrier height can be achieved by extracting the part of purely thermionic emission current from total current.The effect of high temperature measurement on the performance of the 4H-SiC SBD was investigated.The degradation mechanism in high temperature was analyzed.When the diode was tested under 250?C,the ideality factor and Schottly barrier height were changed.Combined current method simulation confirms that the thermionic field emission current(TFE)plays a dominant role in high temperature,which leads to the deviation from the ideal characteristics of SiC Schottky diode.The capacitance characteristics of SiC SBD were investigated and the results showed that the diode could work at high frequency.