低温GaN成核层MOCVD生长工艺对GaN外延薄膜影响的研究
发布时间：2019-05-07 05:06
【摘要】：III族氮化物半导体材料的研究和应用是目前半导体行业的热点。GaN基半导体材料作为第三代半导体材料的代表，在高温、高频、微波、大功率光电子等领域得到了很大的发展，大量的研究也证明以GaN等为代表的宽禁带、直接带隙半导体材料仍有着广阔的发展空间和发展前景。然而由于GaN熔点高，平衡蒸汽压很大，GaN材料的制备极为困难并且成本极高，这也使得GaN的外延生长主要在异质衬底(如蓝宝石)上进行，但异质衬底与GaN之间较大的晶格失配及热失配导致后续生长的GaN外延层具有很高的位错密度(约为108-1010cm2)，晶体质量比较差。这些高密度的位错严重影响了半导体材料的晶体质量和光电性能。为了提高GaN外延薄膜的生长质量，本文从成核层的生长工艺入手，通过对成核层生长时的温度和氨气流量两个工艺参数进行优化，提高了GaN外延薄膜的晶体质量，并对成核层的生长机理和对上层非掺杂GaN外延薄膜的影响机制作了进一步的讨论，其主要的研究成果如下： 首先，本文利用金属有机化学气相沉积(MOCVD)设备在蓝宝石衬底上生长了具有不同成核层生长温度(分别为610℃、630℃、650℃、670℃和690℃)的五组GaN外延薄膜样品，并通过in-situ原位监测以及AFM、HRXRD、PL和HALL等表征手段进行检测。结合实验数据可知，成核层的生长温度对GaN外延薄膜的晶体质量有着重大的影响。只有在适合的温度下，GaN成核层才会在退火后形成大小均一，密度适中的三维形核岛，然后在后续的生长过程中顺利实现从3D生长模式向2D生长模式的转变，最终得到高质量的GaN外延薄膜。在成核层生长温度为650℃时，得到最为光滑致密的GaN外延薄膜，位错密度最低，光电性能最好，带边峰强度最高，，载流子浓度最低，载流子迁移率最高。 除温度外，本文还探究了氨气流量对低温GaN成核层生长过程的影响，以及对后续高温非掺杂GaN外延薄膜晶体质量的影响。本实验仍用Aixtron公司的MOCVD设备，采用两步生长法在蓝宝石衬底上制备了成核层生长时氨气流量不同(分别为A样品400sccm、B样品800sccm、C样品1200sccm、D样品1600sccm、E样品2400sccm)的五组GaN外延薄膜样品。通过对实验所得的样品进行HRXRD、PL、AFM和HALL等测试得知，成核层生长时的氨气流量最优值为800sccm，此时样品刃型位错密度和螺型位错密度均为最低，并且具有最好的光电性能。
[Abstract]:The research and application of III nitride semiconductor materials is a hot spot in the semiconductor industry at present. Gan-based semiconductor materials, as the representative of the third generation semiconductor materials, have been greatly developed in the fields of high temperature, high frequency, microwave, high power photoelectron and so on. A large number of studies have also proved that direct band gap semiconductor materials with wide bandgap represented by GaN et al still have broad development space and prospect. However, due to the high melting point and high equilibrium vapor pressure of GaN, the preparation of GaN materials is very difficult and the cost is very high, which makes the epitaxial growth of GaN mainly on heterogeneous substrates (such as sapphire). However, the large lattice mismatch and thermal mismatch between heterogeneous substrate and GaN lead to high dislocation density (about 108-1010cm2) and poor crystal quality of GaN epitaxial layer. These high density dislocations seriously affect the crystal quality and photoelectric properties of semiconductor materials. In order to improve the growth quality of GaN epitaxial film, the crystal quality of GaN epitaxial thin film was improved by optimizing the temperature and ammonia flow rate during the growth of the nucleation layer from the point of view of the growth technology of the epitaxial layer, and the crystal quality of the epitaxial film was improved by optimizing the temperature and the flow rate of ammonia. The growth mechanism of the nucleation layer and the influence mechanism on the undoped GaN epitaxial film are discussed. The main results are as follows: firstly, the growth mechanism of the nucleation layer and the influence mechanism of the epitaxial film on the undoped layer are discussed. Five groups of GaN epitaxial films with different nucleation temperatures (610,630,650, 670 and 690 鈩
本文编号：2470796
[Abstract]:The research and application of III nitride semiconductor materials is a hot spot in the semiconductor industry at present. Gan-based semiconductor materials, as the representative of the third generation semiconductor materials, have been greatly developed in the fields of high temperature, high frequency, microwave, high power photoelectron and so on. A large number of studies have also proved that direct band gap semiconductor materials with wide bandgap represented by GaN et al still have broad development space and prospect. However, due to the high melting point and high equilibrium vapor pressure of GaN, the preparation of GaN materials is very difficult and the cost is very high, which makes the epitaxial growth of GaN mainly on heterogeneous substrates (such as sapphire). However, the large lattice mismatch and thermal mismatch between heterogeneous substrate and GaN lead to high dislocation density (about 108-1010cm2) and poor crystal quality of GaN epitaxial layer. These high density dislocations seriously affect the crystal quality and photoelectric properties of semiconductor materials. In order to improve the growth quality of GaN epitaxial film, the crystal quality of GaN epitaxial thin film was improved by optimizing the temperature and ammonia flow rate during the growth of the nucleation layer from the point of view of the growth technology of the epitaxial layer, and the crystal quality of the epitaxial film was improved by optimizing the temperature and the flow rate of ammonia. The growth mechanism of the nucleation layer and the influence mechanism on the undoped GaN epitaxial film are discussed. The main results are as follows: firstly, the growth mechanism of the nucleation layer and the influence mechanism of the epitaxial film on the undoped layer are discussed. Five groups of GaN epitaxial films with different nucleation temperatures (610,630,650, 670 and 690 鈩
本文编号：2470796
本文链接：https://www.wllwen.com/kejilunwen/dianzigongchenglunwen/2470796.html
