| As a versatile dielectric material, SrTiO3 is a typical perovskite type structure. It is promising for future generation electrical devices because of high dielectric constant, low dielectric loss and excellent thermal stability. GaN is a third-generation semiconductor, it owns many obvious advantages, such as wide band gap, high saturated electron drift velocity, high thermal conductivity. It is widely used in high-power, high-frequency and high-speed semiconductor devices. Formed by modulation doped, AlGaN/GaN heterostructures have high carrier concentration and electron mobility, and has a very wide range of applications in low-noise high electron mobility transistor (HEMT).While integrating the SrTiO3 and AlGaN with the method of solid-states films, the integrated dielectric material and semiconductor will perform new phenomenon and accelerate the miniaturization and monolithic development of electronic systems.SrTiO3 and GaN have absolutely large lattice mismatch. They are deposited in different method in different circumstance. So it is difficult to epitaxial grow SrTiO3 on GaN directly, on the other hand, the interface diffusion has seriously affected the electrical properties of composite films. In our research, we investigate the epitaxial deposition of SrTiO3/AlGaN/GaN heterojunction with the buffer TiO2, MgO, and Composite buffer TiO2/MgO. When the films are fabricated, we study the electrical properties of thin films. The moving charge density is confirmed by measuring capacitance-voltage with the positive and negative bias temperature treatment. The interface properties are confirmed by high frequency quasi-static (HF-QS) method. We get the optimal growth conditions by the research above. The major elements are following:(1) Deposited the SrTiO3 thin film on AlGaN substrate directly and found that SrTiO3 couldn't crystallize on AlGaN substrate at low temperature. The SrTiO3/AlGaN/GaN heterojunction has a high density of movable charge, which is 2.87×1012/cm2. There is serious interface diffusion, the interface state density(Ns) reach up to 2.66×1013/cm2. The leakage current density is 3.83×10-4A/cm2 at -5V. (2)With the buffer TiO2, we get the highly (111)-oriented SrTiO3 at low temperature. The results show that TiO2 can be used as seed layer and induced the epitaxial growth of SrTiO3 thin film. So the crystal temperature of SrTiO3 is significant reduced. The obtained SrTiO3/TiO2/AlGaN/GaN heterojunction has a low density of movable charge, which is 1.38×1012/cm2. The interface state density(Ns) is 2.44×1012/cm2. The leakage current density is 2.13×10-5A/ cm2 at -5V, which is one orders of magnitude lower than SrTiO3/AlGaN/GaN heterojunction.(3) With the buffer MgO, We get highly (100) -oriented SrTiO3 at low temperature. The results show that MgO has a good interface control function and can effectively block electron injection. The obtained SrTiO3/MgO/AlGaN/GaN heterojunction has a well quality of interface and the interface state density(Ns) is 1.33×1012/cm2. The density of movable charge is 1.02×1012/cm2. The leakage current density is 1.62×10-5A/cm2 at -5V, which is one order of magnitude lower than SrTiO3/AlGaN/GaN heterojunction.(4)With composite buffer TiO2/MgO, we deposited highly (100) -oriented SrTiO3 at low temperature. The results show that composite buffer TiO2/MgO owns the advantages of both. The composite buffer has not only induced the growth of SrTiO3 thin films and reduced the lattice defects, but also blocked the interaction between SrTiO3 and AlGaN diffusion. The SrTiO3/TiO2/MgO/AlGaN/GaN heterojunction has the lowest interface state density(Ns), which is 6.8×1011/cm2.The density of movable charge is 7.67×1011/cm2. Compared to the SrTiO3/AlGaN/GaN heterojunction, the leakage current density is 2.16×10-6 A/cm2, which is two orders of magnitude lower than SrTiO3/AlGaN/GaN heterojunction.At last, we prepared the MOSHEMT and MESHEMT devices by using the films obtained, and explored their output characteristics. |
PDF Full Text Request