氮化铝晶体的制备及应用简介
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One
第一代半导体:以Si,Ge半导体材料为代表的窄带隙半导体;
First generation semiconductor: narrow band gap semiconductor, represented by Si, Ge semiconductor materials;
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Two
第二代半导体:以GaAs,InP半导体材料为代表的二元化合物半导体;
Second generation semiconductors: two - element compound semiconductors, represented by GaAs, InP semiconductor materials;
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Three
第三代半导体:以碳化硅(SiC),氮化镓(GaN),氧化锌(ZnO),金刚石和氮化铝(AlN)为代表的宽禁带半导体材料,具有禁带宽度宽,击穿电场高,热导率高,电子饱和速率高以及抗辐射能力高等优点。
The third generation semiconductor with silicon carbide (SiC), gallium nitride (GaN), Zinc Oxide (ZnO), diamond and aluminum nitride (AlN) semiconductor material with wide band gap as the representative, with wide band gap, high breakdown field, high thermal conductivity, high electron saturation velocity and anti radiation ability etc..
图1 半导体
Figure 1 semiconductors
从第三代半导体材料和器件研究发展现状来看,较为成熟的是SiC和GaN半导体材料,其中SiC技术最为成熟,而ZnO、金刚石和AlN等宽禁带半导体材料的研究尚属起步阶段。但与GaN和SiC相比,AlN具有多种优异性能:
From the third generation of semiconductor materials and devices based on the current situation of the development, mature SiC and GaN semiconductor material, in which SiC technology is mature, while the research of diamond and AlN wide band gap semiconductor material, ZnO is still in the initial stage. But compared with GaN and SiC, AlN has a variety of excellent performances:
✔ 禁带宽度6.2eV,并具有直接带隙,是重要的蓝光和紫外发光材料;
6.2eV, band width, and has a direct band gap, is an important blue light and ultraviolet light emitting material;
✔ 热导率高,熔点高,电阻率高,击穿场强大,介电系数小,是优异的 高温、高频和大功率器件用电子材料;
, high thermal conductivity, high melting point, high resistivity, breakdown field strength, dielectric coefficient is small, with electronic materials of high temperature, high frequency and high power devices excellent;
✔ 沿c轴取向的AlN具有非常好的压电性和声表面波高速传播性能,是优异的声表面波器件用压电材料。
, along the c axis oriented AlN has very good piezoelectric and surface acoustic wave propagating properties of piezoelectric material with excellent surface acoustic wave device.
鉴于上述AlN材料优异的物理性质,AlN晶体是GaN、AlGaN以及AlN外延材料的理想衬底。与蓝宝石或SiC衬底相比,AlN与GaN热匹配和化学兼容性更高、衬底与外延层之间的应力更小,因此AlN晶体作为GaN外延衬底时可大幅度降低器件中的缺陷密度,提高器件的性能,在制备高温、高频、高功率电子器件方面有很好的应用前景,尤其在蓝光-紫外固态激光二极管、激光器、GaN基高电子迁移率晶体管(HEMT)器件和日盲型AlGaN紫外探测器件的衬底方面具有独特优势。
In view of the excellent physical properties of the above AlN materials, AlN crystal is an ideal substrate for GaN, AlGaN and AlN epitaxial materials. Compared with the sapphire or SiC substrate, AlN and GaN, thermal and chemical compatibility is higher, less stress between substrate and epitaxial layer, so the AlN crystal as GaN epitaxial substrate can greatly reduce the density of defects in the device, improve the performance of the device, it has good application prospect in the preparation of high temperature, high frequency and high power electronic devices, especially in the blue and ultraviolet solid-state laser diode, laser, GaN based high electron mobility transistors (HEMT) has the unique advantage of the substrate device and AlGaN based solar blind UV detector.
图2 氮化铝晶片
Figure 2 aluminum nitride wafer
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One
氮化铝晶体的性质
Properties of aluminum nitride crystals
1.1 氮化铝晶体的化学性质
The chemical properties of 1.1 aluminum nitride crystals
在标准大气压下,AlN晶体在1700℃左右开始缓慢分解成Al蒸气和氮气,当温度达到2200℃时AlN迅速分解成Al蒸气和氮气,在不同温度下AlN分解后的分压如图3所示。常压下AlN晶体很难以液相形式存在,在AlN达到熔点之前AlN已经开始分解,这是AlN晶体不能通过熔融法生长的原因,但有研究表明,100大气压下AlN液相可在2800℃出现。AlN粉末在空气中很不稳定,容易与空气中的水蒸气和氧气反应生成氨气和氧化铝。AlN具有很强的抗酸碱能力,酸性环境中AlN可以稳定存在,在碱性环境中AlN少量被腐蚀。300℃时,AlN晶体在KOH和NaOH的1:1熔液中腐蚀3-5min,晶体表面可以观察到六方腐蚀坑等缺陷,但除此之外,未见大量腐蚀的迹象,实验上通过此方法区分AlN的极性面。
At standard atmospheric pressure, AlN crystals begin to decompose slowly into Al vapor and nitrogen at about 1700 degrees. When temperature reaches 2200 degrees, AlN decomposes rapidly into Al vapor and nitrogen. The partial pressure of AlN decomposition at different temperatures is shown in Figure 3. Under normal pressure, AlN crystal is very difficult to exist in liquid phase. Before AlN reaches the melting point, AlN has begun to decompose, which is why AlN crystals can not grow by melting. However, studies have shown that the AlN liquid phase can appear at 2800 AlN at atmospheric pressure. AlN powder is very unstable in the air, and it is easy to react with the water vapor and oxygen in the air to produce ammonia and alumina. AlN has a strong ability to resist acid and alkali, and AlN can be stable in acid environment. In alkaline environment, a small amount of AlN is corroded. At 300 C, AlN crystals corrode 3-5min in the 1:1 melt of KOH and NaOH. Defects such as six party corrosion pits can be observed on the surface of the crystal, but there is not a lot of corrosion. Besides, the polar surface of AlN is distinguished by this method.
图3 AlN-N2系统Al、N的分压与温度倒数的关系
The relationship between the partial pressure of Al and N in Figure 3 AlN-N2 system and the reciprocal of temperature
1.2 氮化铝晶体的物理性质
Physical properties of 1.2 aluminum nitride crystals
AlN晶体有着优异的物理性质,如AlN晶体的宽带隙、高硬度、高热导率和较大的介电常数等,这些性质引起了大家的广泛关注,表1为AlN晶体的物理性质。
AlN crystals have excellent physical properties, such as wide gap, high hardness, high thermal conductivity and large dielectric constant of AlN crystals. These properties have attracted wide attention. Table 1 is the physical properties of AlN crystals.
表1 AlN晶体的物理性质
Table 1 physical properties of AlN crystal
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Two
氮化铝晶体的生长
Growth of aluminum nitride crystals
1956年,Kohn等第一次生长出AlN单晶,直径0.03mm,长度0.3mm;1976年,Slack和McNelly利用升华凝结法(sublimation recondensation)成功生长出AlN晶锭;目前,实验室中已经生长出直径大于2英寸的AlN晶锭,但仍有许多需要解决。
In 1956, Kohn first time the growth of single crystal AlN, diameter 0.03mm, length 0.3mm; in 1976, Slack and McNelly by sublimation condensation method (sublimation recondensation) successfully grown AlN ingot; at present, the laboratory has grown out of AlN ingot diameter greater than 2 inches, but there is still a lot to solve.
AlN晶体在生长过程中的难点主要包括以下两点:
The difficulties in the growth of AlN crystals include the following two points:
✔ AlN晶体具有极高的熔点温度(~3500K)和较大的分解压,正常压力条件下,AlN在熔化前即会发生分解,因此无法从熔体中生长AlN晶体;
AlN crystal, with high melting temperature (~3500K) and high decomposition pressure, normal pressure conditions, AlN before melting will decompose, therefore cannot AlN crystal growth from the melt;
✔ AlN在高温下分解出的铝蒸汽很活泼,易腐蚀坩埚,需要选择耐高温、耐腐蚀的坩埚材料。
Aluminum vapor decomposition at high temperature, AlN is very active, easy corrosion of crucible, crucible material to a high temperature resistant and corrosion resistant.
目前已采用了多种方法制备AlN晶体,如:铝金属直接氮化法、溶液法生长氮化铝晶体、氢化物气相外延法和物理气相传输法。
Many methods have been used for the preparation of AlN crystals, such as direct metal nitridation of aluminum metal, growth of aluminum nitride by solution method, hydride vapor phase epitaxy and physical vapor transport.
2.1 铝金属直接氮化法
Direct nitriding of 2.1 aluminum metal
Al金属直接氮化法的基本反应为高温下金属Al粉末与氮气直接反应生成AlN晶体。化学反应方程式为:
The basic reaction of Al metal direct nitriding is that the metal Al powder reacts with nitrogen directly to produce AlN crystal at high temperature. The chemical reaction equation is as follows:
2Al(s)+N2→2AlN(s)
2Al (s) +N2 - 2AlN (s)
但此方法制备AlN晶体过程中,Al金属粉末与N2反应过程中会产生大量的热,导致反应急剧加速、晶体生长过程难以控制,获得的产物只是AlN晶体粉末。后来Schlessre等通过在N2 气氛中气化金属Al的方法,成功制得面积50mm2的AlN单晶薄片,反应温度2100℃,反应时间2hrs。
However, during the process of preparing AlN crystal, a lot of heat will be generated during the reaction of Al metal powder and N2, which will lead to rapid acceleration of the reaction and difficult control of the crystal growth process. The product obtained is only AlN crystal powder. Later, Schlessre et al. Through the way of gasifying metal Al in N2 atmosphere, the area of 50mm2 AlN single crystal slice was successfully produced, the reaction temperature was 2100 degrees, and the reaction time was 2hrs.
2.2 高氮气压溶液生长法
2.2 high nitrogen pressure solution growth method
AlN具有极高的稳定性和熔点(3800℃),并且在1700℃时AlN粉末开始升华,因此通过传统的熔融法生长AlN晶体几乎是不可能的。
AlN has high stability and melting point (3800 C), and at 1700? C, AlN powder starts to sublimate, so it is almost impossible to grow AlN crystal by traditional melting method.
当压力大于500MPa时,Al与N2高温燃烧反应速率减慢,这是因为N2在高压条件下具有较高的热导率和较大的热容,导致燃烧反应过程中的热量损失增加;当压力大于650MPa时,燃烧反应被完全终止;此外,高压条件下N2的密度较大,有利于减少Al的蒸发和扩散;基于上述机理,Bockowski等利用高氮气压溶液生长法成功制得白色针状AlN单晶,直径1mm,
When the pressure is greater than 500MPa, the reaction rate slowed down Al and N2 high temperature combustion, this is because the N2 has a high thermal conductivity under the condition of high pressure and large heat capacity, resulting in the loss of heat during the combustion reaction increases; when the pressure is greater than 650MPa, the combustion reaction was completely terminated; in addition, the density of N2 under high pressure the larger, helps to reduce the evaporation and diffusion of Al; based on the above mechanism, Bockowski with high nitrogen pressure solution growth method successfully prepared white needle crystal AlN, diameter 1mm,