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The Characterization of Undoped and Mg Doped InN and the Study on Their Rapid Thermal Annealing Properties

Author: WangJian
Tutor: XieZiLi
School: Nanjing University
Course: Microelectronics and Solid State Electronics
Keywords: Ⅲ-Nitrides MOCVD InN XRD dislocation density RTA PL
CLC: TN304
Type: Master's thesis
Year: 2013
Downloads: 24
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Abstract

The Ⅲ-nitride semiconductor material system, including GaN, InN, A1N, together with its ternary alloys and quaternary alloy, has wide applications due to its excellent physical properties. Since the band gap of InN has been testified to be0.7eV in recent years, the band gap of such a system can vary consistently from0.7eV to6.2eV, and the corresponding wavelength covers an extensive spectrum range from near-infrared to ultraviolet. During more than two decades’extensive studies, GaN-based high-power electronic devices as well as short-wavelength light-emitting diodes (LED) and lasing diodes (LD) have become industrial and commercial, which are regarded as a new science and technology revolution. Compared with other Ⅲ-nitride semiconductors, InN has the smallest effective mass, the highest mobility and the highest electron drift velocity. Because of its unique characteristics, InN has attracted lots of attention and is expected to be a very promising material for high-speed and high-frequency electronic and optoelectronic devices.In this thesis, what we focus on are two kinds of InN, undoped and Mg doped, both of which are grown by metal organic chemical vapor deposition (MOCVD). By utilizing X-ray diffraction (XRD), photoluminescence (PL) and other techniques, we analyze the dislocation densities and the effect of rapid thermal annealing (RTA) on their properties separately. Some other electrical and optical properties about the two materials are also given in this paper. The main conclusions are listed as follows:1. The surface morphology of the two materials grown by MOCVD is investigated. With the help of scanning electron microscope (SEM) and atomic force microscope (AFM), the mixed growth mode, which is three-dimensional island mode combine with two-dimensional step-flow mode, is revealed for the InN grown on a GaN buffer layer. Both of the two materials have a rough surface. We also find some hexagonal clusters on the surface of Mg doped InN, which is most likely to be InN after analyzed by energy dispersive X-ray spectroscopy (EDX).2. The dislocation densities of the two materials are investigated based on the mosaic model. The mosaic tilt, twist and correlation lengths of the InN films are determined by using XRD symmetrical and asymmetrical reflections as well as reciprocal spacing mapping (RSM), which will then lead to the screw type and edge type dislocations. For the Mg doped InN, the screw type dislocation Nscrew=4.84×1010cm-2, and the edge type dislocation Nedge=1.87×1011cm-2. While for the undoped InN, Nscrew=7.92×1010cm-2, Nedge=1.01×1011cm-2. Such a result indicates that the edge type dislocation is the predominant type in the InN films.3. From the position of InN diffraction peak obtained from XRD2θ-ω scan and two lattice vibration modes obtained from Raman scattering, we find that the stress in the Mg doped InN film that we grow is smaller than that in the undoped InN film. There is also no sign of In segregation deduced from the result of XRD2θ-ω scan.4. Compared with the dislocations and electron mobility of Mg doped InN in different rapid thermal annealing (RTA) temperatures, we find the crystal qualities are greatly improved at400℃when annealed for30s in N2atmosphere. We suggest that Mg-H bonds are broken and Mg atoms are activated by the RTA treatment, which will compensate the large electron concentration in the film. At the same time, N vacancies, which act as donors, are partly compensated when annealing in N2atmosphere, leading to the reduction of defects and dislocations as well as carrier concentration. Also, the carrier mobility is improved. As to the undoped InN, we find the best RTA temperature is300℃with the same method, which is lower than that of Mg doped InN. This is mainly because Mg atoms need a higher temperature to be activated as acceptors. Finally, we conclude that the residual stress in InN is not changed after annealing based on the fact that there is no obvious shift of the A1(LO) mode for the different annealed samples.5. The PL properties of the undoped InN film are investigated. InN has a high level of background carrier concentration, which makes the Fermi level lie above the conduction band. By nonlinear fitting the PL results, along with the energy band relations, we calculated that the band gap of the undoped InN film is0.67eV and the carrier concentration n=5.4×1018cm-3. Thus we found a connection between PL results and the carrier concentration of InN films. In addition, we studied the dependence of peak position and intensity of PL on temperature by choosing various temperatures. The intensity of photoluminescence decreases as the temperature increases, and the peak position turns out a red shift instead of a non-monotonic variation mentioned in references. Such a difference can be explained by a large full width at half maximum (FWHM) of PL spectra. Also the concentration of carriers and the magnitude of the built-in electric field in the material may have influence on such a result.

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