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Epitaxial Growth Of GaN-based LED Film On Si Substrate And Its Chip Fabrication

Posted on:2018-06-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y H LinFull Text:PDF
GTID:1318330533467133Subject:Materials science
Abstract/Summary:PDF Full Text Request
GaN,which is one of the third generation semiconductor materials,has excellent characteristics such as wide band gap,high electron mobility,and good thermal conductivity,and can be widely used in devices such as optoelectronic semiconductors and high mobility semiconductors.Especially in the field of semiconductor lighting,GaN-based light-emitting diode(LED)has become the mainstream of the lighting market.However,with the large-scale application of GaN-based LED,how to reduce the cost of preparation of LED has become the focus of the market.Based on the cost considerations,the use of single-crystal Si as the substrate for the growth of GaN-based LEDs was proposed by the researchers because the Si substrate has the advantages of mature preparation,large-size substrate,low manufacturing cost and excellent thermal conductivity.All these advantages of Si substrate is capable of reducing the preparation cost of LED,and improving the stability performance of LED devices significantly.So far,the fabrication technology of LED-on-Si has been a big breakthrough,but there are still a series of basic problems in material growth,mechanism research and chip preparation,which restricts the performance of GaN-based LED on Si substrate.Both the growth of high-quality GaN-based LED epitaxial materials and the preparation of high-performance LED chip are still hotspots on reaserch field of LED-on-Si.In this paper,the growth of high-quality GaN-based LED epitaxial materials on Si substrate and the preparation of the chip were carried out.The main achievements are as follows:Firstly,a two-step AlN buffer layer was proposed to solve the problem of "melt-etching".The step-graded AlGaN buffer layer was used to suppress the formation of GaN surface crack.It has been found that the surface coalescence of the AlN buffer layer is the key to preventing "melt-etching" reactions.The study on AlN growth process shows that the high temperature and low V / III ratio can improve the migration of Al atoms and promote the coalescence of AlN.Based on the results of this study,we propose a two-step method for AlN growth.The AlN island growth is formed at the high V/III ratio,and thereby releases the stress in the film,and then AlN islands are promoted to coalescence by using the high temperature,low V / III ratio.As a result a AlN buffer layer whose surface approaches the two-dimensional growth is obtained,and thus successfully preventing the "melt-etching" reaction of Si and GaN,finally to obtain a GaN film with flat surface.In order to solve the problem of cracks,we introduced AlGaN buffer layer and studied the effect of AlGaN buffer layer on stress and crystalline quality of GaN films on Si.It is found that the step-graded AlGaN buffer layer can enhance the compressive stress of the GaN film during the growth process,and thereby counteracting the tensile stress formed during the cooling process,finally to obtain the crack-free Ga N film on the Si substrate.Secondly,several structural of interlayers are used to effectively reduce the dislocation density in GaN films.In this paper,we study the island growth of GaN to promote the bending and annihilation of dislocations.The 3-dimensional(3D)GaN island growth was aroused by high-pressure grown GaN interlayer,and then the AlN and 3D SiN interlayers were introduced into the AlGaN buffer layer by high pressure growth,and thento enhance the island-like growth trend of 3D GaN.The study of the AlN interlayer demonstrates that the introduction of the AlN interlayer under the 3D GaN interlayer can promote the island-like growth of GaN because of the lattice mismatch between AlN and GaN.Furthermore,it is proved that the SiN interlayer deposited on the GaN islands is able to inhibit the lateral growth of GaN island,and thus delaying the healing of GaN islands.Throuth these methods,the dislocations suppression of 3D GaN island growth is enhanced,and thereby to improve the crystal quality of GaN films.Finally,high-quality GaN films were obtained by the above-mentioned three kinds of interlayers.The XRD rocking curves results show that the full-width at half-maximum values of the GaN(0002)and GaN(10-12)of GaN films are 320 and 392 arcsec,respectively,showing excellent crystal quality.Finally,a complete LED epitaxial wafer is grown on a Si substrate,and a vertical structure LED chip is then prepared by removing the substrate in order to solve the problem of light absorption of the Si substrate.In this paper,the InGaN/GaN multi-quantum well structure and the p-GaN layer were continuously grown on the optimized GaN films on Si substrates.Subsequently,the epitaxial Si substrates were removed by substrate transfer and substrate removal technology to prepare the chip of vertical structure.The light extraction rate of LED chips is enhanced by depositing the metal reflective layer and coarsing N-type surface.The results show that the the chip with 1?1 mm2 size is running at the volage of 3.55 V at current of 350 mA,and the light output power of chip is 378.62 mW,showing a good photoelectric performance.At the same time,due to the good heat dissipation performance of the transferred Si substrate,the chip of vertical structure still maintains good photoelectric performance and wavelength stability under the high current(700 mA).In this paper,the effects of AlN,AlGaN buffer layer and several interlayers on the stress control and dislocation suppression of GaN grown on Si substrate were studied in detail.The high quality and crack-free GaN-based LED epitaxial material on Si substrate was realized.And,then the the LED chips of vertical structure are prepared,which provides important guidance for the epitaxial growth of high quality group III nitride material and the preparation of device on Si substrate.
Keywords/Search Tags:Si substrate, gallium nitride(Ga N), light emitting diode(LED), metal-organic chemical vapor deposition(MOCVD), epitaxial growth mechanism
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