张法碧,男,教授,硕士生导师。广西高校引进海外高层次人才百人计划,广西高校千名骨干教师培训计划人选,广西创新创业青年人才培养示范,广西E层次人才;研究领域:微电子与固体电子学。研究方向:紫外探测材料器件、宽禁带半导体材料与器件、二维材料与器件、透明氧化物薄膜与器件、功率器件。主持国家级项目一项,其他项目十余项。在Applied physics letters, Thin solid film, Journal of alloy and compounds等国际著名期刊已发表论文50余篇。成果获得了美国空军研究实验室、美国华盛顿大学、意大利卡利亚里大学等机构的一致好评与引用。曾经获得过国家多媒体课件大赛理工组二等奖,广西教育技术应用大赛特等奖,广西教学成果二等奖。
目錄:
1 Introduction
1.1 Background
1.2 Review of studies on Ga2O3, Ga1-xInx2O3 and AlxGa1-x2O3 films
1.2.1 Ga2O3
1.2.2 Si doped Ga2O3
1.2.3 Ga1-xInx2O3
1.2.4 AlxGa1-x2O3
1.3 Purpose and Outline
2 Film growth and characterization methods
2.1 Film deposition techniques
2.2 Pulsed laser deposition
2.2.1 Basic of pulsed laser deposition
2.2.2 The deposition process
2.2.3 The pulsed laser deposition equipment used in this research
2.2.4 The film growth procedures
2.3 Characterization methods
3 Growth and characterization of Ga2O3 films
3.1 Introduction
3.2 Oxygen pressure influence
3.2.1 Growth rate
3.2.2 Crystal structure
3.2.3 Transmittance and surface morphology
3.2.4 Discussions
3.3 Substrate temperature influence
3.3.1 Crystal structure
3.3.2 Optical properties
3.3.3 Surface morphology
3.3.4 Valence band structure
3.4 Growth time influence
3.5 Annealing effects
3.5.1 Annealing effect on films deposited at RT
3.5.2 Annealing effect on films deposited at 500 oC
3.5.3 Annealing effect on CL spectra
3.6 Conclusions
4 Effect of Si doping on properties of Ga2O3 films
4.1 Introductions
4.2 Si content influence
4.3 Substrate temperature influence
4.4 Oxygen pressure influence
4.5 Conclusions
5 Growth and characterization of Ga1-xInx2O3 films
5.1 Introduction
5.2 Bandgap engineering of Ga1-xInx2O3 films
5.2.1 Growth parameters
5.2.2 Optical properties
5.2.3 Structure and surface morphologies
5.3 Thermal annealing impact on crystal quality of GaIn2O3 alloys
5.4 Toward the understanding of annealing effects on GaIn2O3 films
5.4.1 Influence of annealing gas ambient
5.4.2 Influence of annealing temperature
5.5 Annealing effect on films with different indium content
5.6 Conclusions
6 Growth and characterization of AlGa2O3 films
6.1 Introduction
6.2 The Al content in the film
6.3 Structure of the AlGa2O3 films
6.4 Transmittance and bandgap of the AlGa2O3 films
6.5 Conclusions
內容試閱:
Wide bandgap semiconductor materials have become the hot spot of recent research for the possible using in many fields such as light emitting devices, power devices and flame detectors. Among all the wide bandgap materials, -Ga2O3 film with the monoclinic structure is considered as a promising candidate for its large bandgap and chemical and physical stabilities. And it is also suitable for extreme environment applications such as high temperatures, intense radiation and corrosive environments. However, the bandgap should be tuned to realize high sensitive wavelength tunable photodetectors, cutoff wavelength-tunable optical filters or to introduce shallow impurity levels for good electronic properties.
In Chapter 1, the background including the properties and the review of studies on Ga2O3, Ga1-xInx2O3, AlxGa1-x2O3 and Si doped Ga2O3 were described. The purpose or the motivation of this study was presented.
In Chapter 2, the film growth and characterization methods were introduced.
In Chapter 3, we have investigated the influences of oxygen pressure, substrate temperature and deposition time on the structure and optical properties of Ga2O3 films grown by PLD. The influence of post annealing was also been discussed. 1 The crystal quality and the thickness of films deposited at 600 oC increase with the increasing of oxygen pressure. The growth mode of the films is island mode. 2 By varying the substrate temperature, the evolutions of the structure, surface morphology and bandgap have been clearly clarified. Films deposited at substrate temperature below 400 oC show amorphous structure while those deposited at substrate temperature higher than 500 oC are of high oriented monoclinic structure. 3 The optimized growth substrate temperature and oxygen pressure for our experiment is 500 oC and 0.1 Pa. The growth relationship between the film and the substrate is: sapphire 0001 -Ga2O3 -201 and sapphire [11-20] -Ga2O3 [102]. The obtained -Ga2O3 film is of sixfold in-plane rotational symmetry. The hard X-ray photoemission spectroscopy reveals that the valence band of the crystalline films is mainly due to the hybridization of Ga 4sp. 4 By varying the growth time film thickness, the growth process has been investigated. 5 Post annealing annealing temperature from 700 to 900 oC cannot be used to obtain films with better crystal quality than the film deposited under the optimized growth conditions. The films with post annealing show smaller blueUV emission ratio.
In Chapter 4, we have investigated the Si doping influence on the structure and properties of Ga2O3 films. 1 Ga2O3 films with different Si content were grown on sapphire substrate at 500 oC by PLD. All of the films exhibit smooth surfaces and high transmittances. The films of Si content lower than 4.1 at. % show high -201 oriented monoclinic structure. The carrier density of Ga2O3 film has been increased to 9.11019 cm-3 with conductivity of 2.0 S cm-1 by 1.1 at. % Si doping. Further increase of Si content leads to the decrease of carrier density. 2 By varing the substrate temperature, it is found that film deposited at 500 oC 1 wt.% Si doped shows lowest conductivity and highest carrier density while possesses best crystallinity. 3 Oxygen pressure has no obviously influence on the electrical properties of Si-doped Ga2O3, indicating the oxygen deficiency is not the main origin of the conductive carrier in our study.
In Chapter 5, we showed the growth of crystalline and bandgap tunable Ga1-xInx2O3 films on sapphire 0001 substrate. The elimination of the phase separation was discussed in detail. 1 Optical analysis indicates that the bandgap of the GaIn2O3 films grown by PLD can be tailored from 3.8 eV to 5.1 eV by controlling the indium content. Single phase GaIn2O3 films were obtained although films with nominal In content between 0.2 and 0.5 exhibit phases separation. 2 GaIn2O3 films with nominal In content of 0.3 were deposited on sapphire substrate by PLD at substrate temperatures from RT to 500 oC. The phase separation were observed for the films grown at substrate temperature higher than 300 oC while the films grown at substrate temperature lower than 200 oC revealed homogenous element distributions with amorphous structures. Thermal annealing had no obvious effects on GaIn2O3 films grown at substrate temperature higher than 300 oC. The clusters remained on the surface of the films after thermal annealing treatment. On the other hand, however, by thermal annealing the film deposited at RT in atmosphere, GaIn2O3 film with smooth surface, homogenous element distribution, high orientation crystal and high optical transmittance was successfully obtained. 3 In order to understand the annealing effects, GaIn2O3 films with nominal In content of 0.3 as-deposited in room temperature have been annealed under different gas ambients N2, vacuum, Ar, O2 or at different temperatures 700~1000 oC. It is found that gas ambient and temperature have important influence on crystal quality of annealed GaIn2O3 films. Only oxygen ambient can crystallize GaIn2O3 film and film annealed in 800 oC appears best crystal quality. X-ray photoelectron spectroscopy analysis indicated that oxygen ambient annealing has greatly helped on decreasing the oxygen vacancy. 4 GaIn2O3 films with different nominal In contents from 0.2 to 0.7 annealed at 800 oC under O2 ambient also showed high crystal quality, improved optical transmittance, and smooth surface. Thus, high oriented films with nominal In content from 0.2 to 0.7 without phase separation can be obtained through annealing process. Complementally, high oriented films without phase separation can be obtained in the nominal indium content regions of 0 to 0.1 and 0.9 to 1.0 for the film deposited at 500 oC. By combing the two processes, bandgap tunable high quality GaIn2O3 films throughout the whole indium content range from 0 to 1 can be successfully obtained.
In Chapter 6, bandgap tunable AlGa2O3 films were deposited on sapphire substrates by PLD. The deposited films are of high transmittance as measured by spectrophotometer. The Al contents in films increase linearly with that of the targets. The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of AlGa2O3 films as it is in good agreement with the bandgap values from transmittance spectra. The measured bandgap of AlGa2O3 films increases continuously with the Al content covering the whole Al content range from about 5 to 7 eV, indicating PLD is a promising growth technology for growing bandgap tunable AlGa2O3 films.