The Preparation And Field Emission Properties Of Ge Doped GaN Nanowires

As a well-known ?–? semiconductor material,Gallium nitride(GaN)has been widely studied because of its intrinsic structure.With a direct large band gap(?3.4 e V),allowing it to be used in optoelectronic devices such as light emitting diodes and laser diodes in the blue to ultraviolet region.Being the neighbor element of Ga in the periodic table,Ge atom has a similar size and hence can be expected to be incorporated into the GaN lattice without significant lattice distortion.In addition,it is reported that the intrinsic GaN bulk has a low electron affinity of2.7-3.3e V,which has attracted a lot of attention as a cathode material of field emission devices.There are rare experimental and theoretical reports about Ge-doped GaN nanowires,we will investigate the optimization of field emission properties of the Ge-doped GaN nanowires,including theoretical calculation and experiment in this work.Theoretically,we have investigated how germanium concentration affects the electronic structures and field emission properties of Ge-doped GaN nanowires by the basis of density functional theory(DFT)calculations.The calculated results show that the impurity level can play the role of transition level in the electronic transport process,and the synthesis of Ge-doped GaN nanowires becomes more difficult due to the much larger formation energy required with increase of the germanium concentration.In addition,the calculations of the field emission properties indicate that Ge-doped GaN nanowires have minimum work function when the impurity concentration is about 4.2 atom %,which will be used as a valuable candidate for the future field emission electron sources.Experimently,we first investigate the synthesis of Ge-doped GaN nanowires using chemical vapor deposition(CVD)method,and discuss the influencing factors on preparation of Ge-doped GaN nanowires,like the germanium concentration,and the reaction temperature.X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscope(TEM)were used for characterizing the different concentrations Ge-doped GaN nanowires.Then,we test the field emission properties of Ge-doped GaN nanowires with different doping concentration using the field emission devices,and conclude that the field emission properties of Ge-doped GaN nanowires is better than the pure GaN nanowires.Combined with the result of theoretical calculation,we analyzed that the improvement of the field emission properties is due to the decrease of work function(WF)of the Ge-doped GaN nanowires.