Study On GaN-based Enhencement-mode Devices And Regrowth Of AlGaN/GaN Heterostructure

GaN-based electronic devices are excellent candidates for high power and highfrequency applications at elevated temperatures owing to their superior materialproperties. Because of the strong polarization charge exists in AlGaN/GaNheterostructures, most of the AlGaN/GaN HEMTs demonstrated so far are normally on.E-mode GaN HFETs enable a circuit to be simple, because the voltages applied to thegate and drain electrodes can be of a single polarity, and safety components can beomitted. E-mode GaN HFETs have another benefit whereby various monolithicintegrated D-/E-mode digital circuits can be realized. Furthermore, E-mode devices aredesirable for high-voltage and high-power switching applications in which safety is acritical issue.In this paper, the novel E-mode devices and the regrowth of AlGaN/GaN arestudied by method of theory simulation and experiment. The main work andconclusions are as follows:1. The E-mode AlGaN/GaN HEMT with groove-type channel is simulated. Theresults show, this device exhibits a high threshold voltage with high maximum draincurrent density. Meanwhile, the threshold voltage decrease linearly along with thethickness of the regrown lateral AlGaN, illustrate that the threshold voltage can be goodcontroled.2. The simulation of the E-mode AlGaN/GaN device with discontinuous-channel iscompleted. It is concluded that the device can work normally off and obtain high draincurrent density in the meantime, it also shows a satisfactory transconductance. Inaddition, it is found that the threshold voltage can be adjusted by changing the thethickness of the regrown lateral GaN.3. Regrow AlGaN/GaN on GaN substrate after ICP etch is investigated. It is shown,the ICP etching damage make electrical characteristics of the samples deteriorated, thesurface morphology become worse, and strong yellow luminescence (YL) is observedowing to the large number of defects introduced during regrowing. It is also concludedthat the regrowth can reduce the threading dislocation density effectively, while theetching damage cause a harmful effect on the reduction.The research on RIE etch show that, the etching damage get the surfacemorphology bad, and the reduction of threading dislocation density by the regrowth process is weakened. However, Compared with samples with ICP etch, the regrownsample after RIE etch present better electrical characteristics, and without strong yellowluminescence, explain that RIE has obvious advantages relative to ICP during theregrowing.4. Regrow AlGaN/GaN on GaN substrate after RIE etch and the etching damageare studied, in order to reduce the etching damage, the sample was annealed. The resultsshow, RIE etch of GaN result in large surface damage, which can be repaired to acertain extent by proper annealing treatment. The regrowth can improve the surfacemorphology of the samples, this improvement is particularly obvious for the sampleannealled. Besides, the etching damage lead to increasing of the threading dislocationdensity, while anneal can reduce the damage and the regrowth can reduce the threadingdislocation density, it is proved that the treatment with anneal do help to weaken theetching damage.