JP2004335635A - Nitride semiconductor thin film device employing slightly-tilted substrate, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain surface homology suitable for a purpose by simply controlling the angle of a slightly-tilted substrate. <P>SOLUTION: Using a sapphire slightly-tilted substrate having an off-angle of 0.5° or less, a plurality of nitride semiconductor films having flatness in an atomic scale are fabricated by a molecular beam epitaxy method to manufacture a nitride semiconductor device. Further, an optical device or an electronic device element of the nitride semiconductor device is fabricated by using a linear step of the atomic scale. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nitride semiconductor device using a vicinal substrate, a method for manufacturing the same, and applications thereof.
[0002]
[Prior art]
At present, the mainstream is to use a sapphire substrate and form thereon a nitride semiconductor thin film and a device based thereon. However, the difference between the lattice constants of the nitride semiconductor and the sapphire substrate is large, about 16%. Therefore, crystal growth of a nitride semiconductor is difficult, and a high-quality crystal satisfying the requirements of device application cannot be obtained. In particular, a nitride semiconductor thin film grown by molecular beam epitaxy (MBE), which is often used for crystal growth of other III-V semiconductors (for example, GaAs or InP materials), has a quality suitable for device application. is not.
[0003]
FIG. 9 shows an AFM photograph (5 × 5 μm) of a thin film surface obtained by growing a thin film on a normal Just Sapphire (0001) substrate by MBE. FIG. 9A shows the surface when an AlN (aluminum nitride) thin film is grown on a just sapphire (0001) substrate, and FIG. 9B shows the case where a GaN (gallium nitride) thin film is further grown thereon. Surface. It can be seen that there are irregular steps on the surface of the AlN thin film, indicating a spiral growth (FIG. 9A). Further, the surface of the GaN thin film grown thereon has many grains, but no steps are observed (FIG. 9B).
[0004]
As described above, the dislocation density is high (about 10 ¹⁰ / cm ² ) in the thin film, and many grains exist on the uneven surface. Obviously, these drawbacks cause a great hindrance to the fabrication of device heterostructures. For example, when fabricating an AlGaN / GaN heterostructure or an InGaN / (Al, Ga) N quantum well structure, the unevenness of the interface has a significant adverse effect on the characteristics of the fabricated structure. In addition, high-density dislocations in a large number of Glen structures and the like become the centers of electron traps and hinder realization of high mobility of device carriers.
[0005]
[Problems to be solved by the invention]
As described above, the conventional crystal growth technique has a very disadvantageous aspect in producing a nitride semiconductor and a heterostructure thereof, but this has a serious problem in handling a conventional substrate and cannot be overcome only by the MBE growth method. It is. In order to solve this problem, there is a need for a method for realizing an ultra-flat surface of a nitride semiconductor grown by selecting a substrate and reducing the dislocation density. In order to realize an ultra-flat nitride semiconductor film surface by the MBE method, new technologies and ideas must be introduced.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a nitride semiconductor device in which a plurality of nitride semiconductor films are formed into a flat film on an atomic scale by a molecular beam epitaxy method using an off-angle inclined substrate forming a monoatomic layer linear step, and Provide a recipe.
Further, the nitride semiconductor device can be applied to an optical device or an electronic device device and a method of manufacturing the same.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
FIG. 1 is a schematic view of a nitride semiconductor (cross section) having an ultra-flat surface manufactured by the manufacturing method of the present invention. In the figure, 1 is a vicinal substrate, 2 is an AlN thin film (buffer layer or epilayer), 3 is a GaN thin film, and α is the off angle of the vicinal substrate. The surface of the vicinal substrate 1 uses (0001). The sloping substrate material is sapphire (Al ₂ O ₃ ).
[0008]
In the experimental example, a thin film is grown on a sapphire (0001) substrate with a tilt angle of 0.25 ° to 2 ° by a RF-MBE method (an MBE method using a plasma source and an evaporation source) on a slightly tilted substrate. The surface flatness was observed.
[0009]
As a film growth method, first, a sapphire substrate is nitrided by nitrogen plasma in an MBE chamber. At that time, the substrate temperature is 250 ° C. and the nitriding time is within 2 hours. The plasma power is 350 watts and the nitrogen flow rate is 3 ccm. After nitriding, the substrate temperature is raised to 700 ° C., and Al flux is supplied to the substrate together with N plasma to form an AlN (aluminum nitride) thin film as a buffer layer on the substrate, and then Ga flux is supplied to the substrate together with N plasma. Then, a GaN (gallium nitride) thin film is grown on the AlN thin film. The growth rates of the AlN thin film and the GaN thin film are about 0.4 μm / hr and 0.6 μm / hr, respectively.
[0010]
When the growth temperature is set to 700 ° C. and the AlN epitaxial layer is grown for 1 hour on the nitrided vicinal sapphire substrate, the thickness becomes about 400 nm. The AlN thin film shows two-dimensional growth from the beginning to the end of growth, and it can be seen from real-time observation that the RHEED pattern shows a streak pattern all the time. The surface of the grown AlN thin film is evaluated by AFM (atomic force microscope).
[0011]
2 to 4 show AFM photographs of the surface of the AlN thin film obtained by the above growth method. 2 (a) is an off-angle 0.25 ° substrate, (b) is an off-angle 0.3 ° substrate, FIG. 3 is an off-angle 0.5 ° substrate, FIG. 4 (a) is an off-angle 1.0 ° substrate, FIG. 4B shows the surface of the AlN thin film grown on the substrate having an off angle of 2.0 °.
[0012]
In the case of the sapphire substrate having a slightly inclined off angle of 0.25 ° or 0.3 ° (FIGS. 2A and 2B), uniform linear steps are observed, but spiral steps are partially formed. Observed. The height of these steps is a monoatomic layer. In the case of the slightly inclined substrate having an off angle of 0.5 °, a fine grain of a linear step is observed, but almost no spiral step is observed (FIG. 3). In the case of a vicinal substrate having an off angle of 1 ° or 2 ° (FIGS. 3 (a) and 3 (b)), monoatomic layer and polyatomic layer steps are mixed to form a macrostep (giant step) surface. I have.
[0013]
Next, when the growth temperature is set to 700 ° C. and a GaN epitaxial layer is grown on the grown AlN thin film for 1 hour, the thickness becomes about 600 nm. The GaN thin film shows two-dimensional growth from the beginning to the end of growth, and it can be seen from the real-time observation that the RHEED pattern shows a streak pattern all the time. The surface of the grown GaN thin film is evaluated by AFM.
[0014]
5 and 6 show AFM photographs of the surface of the AlN thin film obtained by the above-mentioned growth method. 5A shows an off-angle substrate of 0.25 °, FIG. 5B shows an off-angle substrate of 0.3 °, FIG. 5C shows an off-angle substrate of 0.5 °, and FIG. FIG. 6B shows the surface of an AlN thin film grown on a 1.0 ° substrate and a 2.0 ° off-angle substrate.
[0015]
In the case of the vicinal substrate having the off angles of 0.25 ° and 0.3 °, uniform linear steps having a step height of a monoatomic layer and spiral steps are sometimes observed (FIG. 5A). , (B)). In the case of a slightly inclined substrate having an off angle of 0.5 °, a fine grain of a linear step is observed, but a spiral step is not observed (FIG. 5C). In the case of a vicinal substrate having an off angle of 1 ° or 2 °, a step of a monoatomic layer and a step of a polyatomic layer coexist to form a macrostep surface (FIGS. 6A and 6B).
[0016]
From the above results, in order to obtain a linear step with a monoatomic layer height on the surface of the AlN thin film and the GaN thin film, it is a necessary condition that the fine inclination angle is 0.5 ° or less. In order to achieve this, it is necessary that the slight inclination angle be larger than 0.5 °.
[0017]
In the first embodiment, the GaN thin film is grown on the AlN thin film. However, it goes without saying that the GaN thin film may be grown directly on the inclined substrate. In the first embodiment, silicon carbide, ZnO, or silicon may be used for the vicinal substrate, and a nitride semiconductor containing In (for example, InGaN or InAlN) may be used as a nitride semiconductor thin film material.
In this case, the semiconductor thin film element may use other epitaxy other than the MBE growth method, for example, a MOCVD (Metalorganic chemical vapor deposition) method.
[0018]
The following semiconductor structure can be manufactured using the surface of the semiconductor thin film.
(Example 2)
Since GaN (Quantum dots) can be produced using the SK (Transki-Krastanov) growth mode at the step edges of well-arranged AlN thin films, quantum dots arranged one-dimensionally along the step edges can be produced. (See FIG. 7).
[0019]
(Example 3)
Utilizing a GaN epitaxial layer having a monoatomic layer step on the surface, (In, Ga, Al) N / (Al, Ga) N quantum wells are formed on the surface, and a high-performance optical device (light emitting diode, Laser diode).
[0020]
(Example 4)
A GaN epitaxial layer having a monoatomic layer step on the surface is used, a GaN / (Al, Ga) N quantum well is formed on the surface, and a communication device using a transition between subinterbands can be manufactured.
[0021]
(Example 5)
By using a GaN epitaxial layer having a monoatomic layer step on the surface and forming an (Al, Ga) N / GaN heterostructure on the surface, high two-dimensional electron gas mobility can be expected. Thereby, a high-frequency, high-output electronic device can be manufactured.
[0022]
(Example 6)
FIG. 8 shows that a GaN / (Al, Ga) N superlattice is formed on an AlN film having linear macrosteps on an inclined substrate, and GaN quantum wires can be formed along the edges of the macrosteps. Thus, application of a nitride semiconductor device using a quantum wire having a quantum confinement effect can be expected.
[0023]
【The invention's effect】
With very simple control of the substrate tilt angle, it is easy to obtain a surface homology suitable for the purpose of application.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a semiconductor structure produced by the method of the present invention.
FIG. 2 is an AFM photograph (No. 1) of the surface of an AlN thin film grown on an inclined substrate.
FIG. 3 is an AFM photograph (No. 2) of the surface of an AlN thin film grown on an inclined substrate.
FIG. 4 is an AFM photograph (No. 3) of the surface of an AlN thin film grown on an inclined substrate.
FIG. 5 is an AFM photograph (No. 1) of a GaN thin film surface grown on the AlN thin film of FIG. 2;
FIG. 6 is an AFM photograph (No. 2) of a GaN thin film surface grown on the AlN thin film of FIGS. 3 and 4;
FIG. 7 shows a one-dimensional array of quantum dots made along a step edge.
FIG. 8 shows a GaN quantum wire produced along a macrostep.
FIG. 9 is an AFM photograph of the surface of an AlN thin film grown on a Just substrate and the surface of a GaN thin film grown on an AIN film.
[Explanation of symbols]
1 Micro-tilt substrate 2 Nitride semiconductor film (buffer layer)
3 Nitride semiconductor film

Claims (4)

A nitride semiconductor thin film element using an off-angle inclined substrate for forming a monoatomic layer linear step. An optical device or an electronic device element using an off-angle inclined substrate that forms a monoatomic layer linear step. A method for manufacturing a nitride semiconductor device, comprising: manufacturing a nitride semiconductor thin film on a tilted off-angle substrate forming a monoatomic layer linear step by using a molecular beam epitaxial method or another epitaxial growth method. A method for manufacturing an optical device or an electronic device element, wherein a nitride semiconductor thin film is formed on a tilted off-angle substrate forming a monoatomic layer linear step by using a molecular beam epitaxial method or another epitaxial growth method.

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