Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2002-11-01
2004-11-09
Trinh, Michael (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S046000, C438S029000, C438S962000
Reexamination Certificate
active
06815242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having quantum dots and a method of manufacturing the same.
2. Description of the Prior Art
With the progress of semiconductor process, the film forming technology and the fine pattern technology in nano scale are going to be employed to form the semiconductor device. As such film forming technology and such fine pattern technology make progress, the integration density of the semiconductor integrated circuit can be improved and also the devices utilizing the quantum-mechanical effect, e.g., HBT (Hetero Bipolar Transistor), the quantum well laser, etc. are put to practical use. In addition, of next generation devices which employ new material are studied in recent years. For example, the quantum dot memory which employs the hole burning effect has been proposed, in Shunichi Muto, Jpn. J. Appl. Phys. Vol.34 (1995) pp. L210-L212.
In recent years, the quantum dot is observed with interest as ultimate structure utilizing the quantum-mechanical effect. The quantum dot is an extremely fine potential box in which quantum confinement of the carriers occurs three-dimensionally. The quantum dot has the state density like a delta function. And, only two carries enter into the ground level of one quantum dot.
As one of the devices utilizing such characteristic of the quantum dot, it is proposed to employ the quantum dot in the active region of the semiconductor laser.
In the semiconductor laser having the quantum well structure, the limits of improvement of the oscillation threshold current and the temperature characteristic of the threshold current are pointed out. However, efficiency in mutual action between the electron/hole and the light can be increased up to the utmost limits by applying the quantum dot to the active layer, and thus the oscillation threshold current and the temperature characteristic of the threshold current can be improved.
In addition, the blue chirp modulator, the wavelength converting device, the single electron transistor, or the quantum dot memory utilizing the hole burning effect has been proposed. The formation of next generation devices by utilizing the quantum dot are studied energetically.
As the technology for forming such quantum dot, the fine pattern technology is employed. For example, the lithography method using the electron beam, the forming method on the bottom of the tetrahedral hole, the method of utilizing the lateral growth on the finely inclined substrate, or the atomic manipulation method utilizing the STM (Scanning Tunneling Microscope) technology has been proposed. The structure of the quantum dot formed at a vertex of the pyramidal crystal is written in U.S. Pat. No. 5,313,484, and the method of forming the quantum dot on the inner surface of the tetrahedral hole is written in U.S. Pat. No. 5,656,821.
Since those methods have a common feature to work artificially, they have such an advantage that the quantum dot position can be controlled arbitrarily. However, the number density of the quantum dots cannot exceed the accuracy limit of the fine pattern technology and also the uniformity of the quantum dots is extremely low.
As the new technology serving as the break-through to form the quantum dot, the technology for self-forming the quantum dot has been found recently. This technology utilizes the phenomenon that the three-dimensional fine structure (quantum dot) can be self-formed by vapor-epitaxial-growing the semiconductor having the lattice mismatching under certain conditions. This method is extremely easy to perform rather than the fine patterning. In addition, the resultant quantum dots can have the very high uniformity beyond the accuracy limit of the artificial work technology, and have the high number density and the high quality.
Such technology is described in Istavan Daruka et al., PHYSICAL REVIEW LETTERS, Vol.79, No.19, 10 November 1997. Devices such as the semiconductor laser, for example, using such self-formed quantum dot are actually reported and a possibility of the quantum dot device becomes practical.
Several forming modes in the self-formation of the quantum dot have been known. The best-known forming mode is,a mode called the Stranski-Krastanov mode (referred to as an “S-K mode” hereinafter). In this mode, the semiconductor crystal which is epitaxially grown is grown two-dimensionally at the beginning of the growth but grown three-dimensionally at the stage beyond the elastic limit of the film. This mode can be most easily achieved in the self-forming modes and thus employed normally. According to this mode, the quantum dots can be formed at the high number density.
FIG. 1
shows the situation that InAs dots
102
which are self-formed on a GaAs substrate
101
are covered with a GaAs layer
103
.
In addition, a mode called the Volmer-Webber mode is known as another mode. In this mode, the semiconductor crystal is grown three-dimensionally from the beginning without the initial two-dimensional growth. It is said that normally this mode occurs at the lower temperature than the S-K mode. However, it is hard to form the dots with high quality and therefore the study of this mode is not actually conducted.
Furthermore, as the new dot forming method utilizing the self-forming mode, a closely stacking. method attracts the skilled person's attention. The closely stacking method is such a method that the big height quantum dots can be formed by laminating the three-dimensional structures, which are formed by the already-mentioned method, via the intermediate layer having a small thickness, through which the carriers are tunneled, along the growing direction to be put together as a lump respectively. According to this method, the quantum dots with the high uniformity can be formed.
In this manner, various methods have been found for the technology for forming the quantum dots. However, if the application of the quantum dot to the devices is considered, it is indispensable to control the energy of the quantum dots.
For example, if the case where the semiconductor laser using the quantum dots is applied to the laser light source for the optical communication is considered, the semiconductor laser whose emission wavelength is 1.3 &mgr;m (0.95 eV) or 1.55 &mgr;m (0.8 eV) must be formed. However, if the InAs or InGaAs quantum dots are formed on the GaAs substrate, the bandgap energy is about 1.1 to 1.3 eV. As a result, it is impossible to employ such quantum dots in the optical communication.
Moreover, in the case of the quantum dots formed by the closely stacking method, similarly the bandgap energy is about 1.1 to 1.3 eV if the InAs or InGaAs quantum dots are formed on the GaAs substrate, like the case of the single S-K mode. As a result, it is impossible to employ such quantum dots in the optical communication.
Still other subjects for the practical use of the device become apparent. There are the temperature dependency of the quantum dot energy as one of such subjects. Normally, the energy is reduced when the temperature is increased, and such temperature change affects the device characteristic. For example, if the low temperature state shown in FIG.
2
A and the high temperature state shown in
FIG. 2B
are compared with each other, the crystal lattice strains between the quantum dots
2
and peripheral crystals
1
,
3
become different.
The reason for the temperature change of the energy is intrinsic. This is because the lattice constant of the semiconductor crystal depends on the temperature and thus the bandgap is changed according to the change of the lattice constant.
That is, such phenomenon occurs in not only the quantum dot but also the quantum well. In order to overcome such phenomenon, search of new material system is carried on, but such search has not come up to the success yet.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device in which an emission wavelength of qu
Ishikawa Hiroshi
Mukai Kohki
Trinh Michael
Westerman Hattori Daniels & Adrian LLP
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