GaN is a very stable compound, but also a hard high melting point material, the melting point of about 1700 ℃, GaN has a high degree of ionization, in the Ⅲ-Ⅴ compounds is the highest (0.5 or 0.43). At atmospheric pressure, GaN crystals are generally hexagonal wurtzite structures. It has 4 atoms in a cell, and the atomic volume is about half that of GaAs. Because of its high hardness, but also a good coating protection materials.
At room temperature, GaN is insoluble in water, acids and bases, and is dissolved at very slow rates in hot alkaline solutions. NaOH, H2SO4 and H3PO4 can quickly corrode poor quality GaN, can be used for these low quality GaN crystal defects detection. GaN in HCL or H2 gas, at high temperatures show unstable characteristics, and in N2 gas is the most stable.
There are two kinds of crystal structures of GaN, which are wurtzite structure and sphalerite structure.
The electrical properties of GaN are the main factors that affect the device. The unintentionally doped GaN is n-type in all cases, and the electron concentration of the best sample is about 4 x 1016 / cm3. In general, the P-type samples prepared are highly compensated.
Many research groups have been engaged in this research work, which reported that the highest mobility of GaN data at room temperature and liquid nitrogen temperature were μn = 600cm2 / v · s and μn = 1500cm2 / v · s, the corresponding current The sub-concentration is n = 4 x 1016 / cm3 and n = 8 x 1015 / cm3. In recent years, the electron concentration of MOCVD deposited GaN layer is 4 × 1016 / cm3, <1016 / cm3; the result of plasma activation of MBE is 8 × 103 / cm3, <1017 / cm3.
The undoped carrier concentration can be controlled in the range of 1014 to 1020 / cm3. In addition, the doping concentration can be controlled in the range of 1011 to 1020 / cm3 by the P-type doping process and the low-energy electron beam irradiation or thermal annealing treatment of Mg.
People are concerned about the characteristics of GaN, aimed at its application in Blu-ray and violet-emitting devices. Maruska and Tietjen first accurately measured the GaN direct gap energy of 3.39 eV. Several groups studied the dependence of GaN bandgap and temperature, and Pankove et al. Estimated the empirical formula for a bandgap temperature coefficient: dE / dT = -6.0 × 10-4eV / k. Monemar measured the basic bandgap of 3.503eV ± 0.0005eV at 1.6kT for Eg = 3.503 + (5.08 × 10-4T2) / (T-996) eV.
In addition, there are many people studying the optical properties of GaN.
New electronic devices
GaN material series has a low heat generation rate and high breakdown electric field, is the development of high-temperature high-power electronic devices and high-frequency microwave devices important material. At present, with the MBE technology in the application of GaN materials and the progress of key thin film growth technology, the successful growth of a variety of heterogeneous GaN structure. (MEMS), such as metal field effect transistor (MESFET), heterojunction field effect transistor (HFET), modulation doped field effect transistor (MODFET), are fabricated by GaN material. The modulation of the doped AlGaN / GaN structure has high electron mobility (2000cm2 / v · s), high saturation rate (1 × 107cm / s), lower dielectric constant, is the preparation of microwave devices priority material; GaN Wide band gap (3.4eV) and sapphire and other materials for the substrate, good heat dissipation, is conducive to the device under high power conditions.
GaN material series is an ideal short wavelength light emitting device material, GaN and its alloy band gap covered from red to ultraviolet spectral range. Since 1991, Japan developed the homogeneous junction GaN blue LED, InGaN / AlGaN double heterojunction ultra-bright blue LED, InGaN single quantum well GaNLED have come out. At present, Zcd and 6cd single quantum well GaN blue and green LED have entered the mass production stage, thus filling the blue LED on the market for many years blank. LED luminous efficiency as a symbol of the development process shown in Figure 3. Blue light-emitting devices in the high-density optical information access, all-optical display, laser printers and other fields have a huge application market. With the deepening of the research and development of the group III nitride materials and devices, GaInN ultra-high blue light and green LED technology have been commercialized. Now the world’s major companies and research institutions have invested heavily in the development of blue LED The ranks of competition.
For GaN materials, since the substrate single crystal has not been solved, the heteroepitaxial defect density is quite high, but the device level has been practical. In 1994, Nichia Chemical made 1200mcd LED, made in 1995 and Zcd blue (450nmLED), green 12cd (520nmLED); Japan in 1998 to develop a wide bandgap nitride material development LED 7 years plan, its The goal is to develop in 2005 sealed in the fluorescent tube, and can send white light of high-energy UV LED, this white LED power consumption is only 1/8 of incandescent, fluorescent lamp 1/2, its life is traditional Fluorescent lamp 50 times to 100 times. This proves that the development of GaN materials has been quite successful, and entered the practical stage. InGaN alloy, InGaN / AlGaN double junction LED, InGaN single quantum well LED, InGaN multi-quantum well LED, etc. have been successfully developed. InGaNSQWLED6cd high brightness pure green brown, 2cd high brightness blue LED has been produced, the future, and AlGaP, AlGaAs red LED combination to form a bright full color display can be achieved. So that the three primary colors mixed white light source also opens a new application areas, with high reliability, long life LED characteristics of the era will come. Fluorescent and light bulbs will be replaced by LED. LED will become the leading product, GaN transistors will also be with the material growth and the development of device technology and the rapid development of a new generation of high-temperature high-power devices