Research On Material And Device Of GaN Schottky Barrier Diode

Gallium nitride with wide bandgap has excellent electrical characteristics and plays a significant role in the field of high frequency and high power applications.In addition,GaN belongs to III-V semiconductor materials,which has a large bandgap,high breakdown electric field,high thermal conductivity,strong corrosion resistance anti-irradiation capability and other unique advantages.Thus,the research on GaN material and device have been rapidly developed in the past ten years.Both the growth of GaN-based material and the device technology have been improved.However,the device performance mainly depends on material quality and process level.As we all know,sapphire substrate with mature technology as one of the most widely used substrate for heteroepitaxial GaN has good stability,and the patterned sapphire substrate?PSS?structure is widely used in LED.The PSS is wished to be used in Schottky barrier diode?SBD?to further explore the application potential of GaN.This paper systematically analyzes the characteristics of N-type GaN grown on sapphire substrates,further studies the mechanism of annihilation of dislocations on PSS.The effects of SiH₄ flux on GaN electrical properties and stress characteristics are studied.The etch process is studied and GaN SBD is fabricated.The main results are as follows:Firstly,the properties of GaN grown on different type of sapphire substrate are studied.Based on MOCVD method,GaN material is grown on PSS and planar sapphire substrate respectively.The result shows that GaN on PSS with better material quality has clearer atomic steps than that on planar sapphire substrate.What's more,the dislocation density of GaN on PSS is reduced by 3 times with better crystal quality than GaN on planar sapphire substrate.The decrease of dislocation density of GaN on PSS is because dislocation extension direction in the GaN epitaxial layer is changed from vertical to lateral,realizing that laterally grown dislocations are quickly annihilated.In addition,GaN on planar sapphire substrate had a stronger yellow luminisence phenomenon because of higher dislocation density and slightly rougher surface.Secondly,the effects of SiH₄ flow rate on GaN characteristics are investigated.When the flow rate is set to 50 sccm,120 sccm and 300 sccm respectively,the sample's mobility increases from 70 cm²/V·s to 165 cm²/V·s first,and then dropes to 120 cm²/V·s.According to our analysis,since the amount of Si-doped sample is small thatt the effect of ionized impurity scattering is weaker causing increased carrier mobility.As the amount of Si is increased,the effect of ionized impurity scattering is enhanced with decreased carrier mobility.In addition,the stress of sample decreases with increasing SiH₄ flow rate.Thirdly,the etch process of fabricating GaN SBD is investigated.When isolation etching is performed first,etching SiO₂ mask take so much time that photoresist is destroyed.In addition,there are two relatively high side peaks on the edge.When the mesa etching is performed first,the presence of the mesa would make photoresist non-uniform without affecting properties of device.Moreover,the two methods of etching make brightness of mesa different.According to the results,the SBD in this paper is performed mesa etching followed by isolation etching.Fourth,the characteristics of GaN SBD are disscussed.As the temperature increases from25°C to 125°C,the forward turn-on voltage of GaN SBD decreases from 0.573 V to 0.501V,and the barrier height decreases from 0.896 eV to 0.732 eV.When W is used as the anode metal,the device turn-on voltage is reduced from 0.9 V to 0.47 V,which is reduced by about half compared to Ni/Au.After the field plate is used,the reverse current of the device is reduced by about 3 orders of magnitude,that is,the field plate effectively reduces the reverse leakage current and realizes the preparation of the device with low leakage current.