1. Field of the Invention
The present invention relates to a semiconductor light emission element using a nitride semiconductor, a semiconductor composite element and a process for producing a semiconductor light emission element.
2. Description of the Related Art
Wide band gap semiconductors have been receiving attention as a semiconductor for a blue light emission element in recent years (S. Nakamura, T. Mukai and M. Senoh, Jpn.J. Appl. Phys., vol. 30, L1998 (1991); and S. Nakamura, M. Senoh, S. Nagahama, N. Iwata, T. Yamada, M. Matsushita, Y. Sugimoto and H. Kiyoku, Appl. Phys. Lett., vol. 69, p. 1477 (1996)). Among them, nitride semiconductors (nitride compound semiconductors) are receiving attention as the wide band gap semiconductor.
However, the nitride semiconductors are often produced by a two-step growth, in which a low temperature buffer layer is firstly formed by using a sapphire substrate, and after increasing the temperature to about 1,000xc2x0 C., crystal growth is carried out at a high temperature of 1,000xc2x0 C.
With respect to silicon semiconductors, which constitute major portion of semiconductor elements, such as LSI, there has been an attempt that light is emitted from silicon to carry out transmission between chips and within a chip with light (K. D. Hirschman, L. Tsybeskov, S. P. Duttagupta and P. M. Fauchent, Nature, vol. 384, p. 338 (1996) and S. Fujita and N. Sugiyama, Appl. Phys. Lett., vol. 74, p. 308 (1999)).
However, silicon cannot emit light as it is because it is an indirect transition semiconductor. Therefore, direct transition III-V compound semiconductors (nitride semiconductors), which emit light, are formed on silicon, but it is the current situation that there is a problem in that crystals of high quality cannot be grown. It is considered that this is because there are excess bonding linkages left severed (dangling bonds) at the junction interface of the two different semiconductors having different lattice constants and they form interface levels. Particularly, in the case where there is a large difference in thermal expansion coefficient between the two semiconductors, it is considered that large stress is formed after cooling because a high temperature is applied upon forming the nitride semiconductor, whereby not only the formation of junction defects is accelerated, but also structural defects, such as cracking, crazing and interfacial exfoliation, are caused.
It is the current situation of the semiconductor light emission element obtained by forming the direct transition III-V compound semiconductors (nitride semiconductor), which emit light, on silicon, that the characteristics of the junction interface are deteriorated by the formation of a large amount of interfacial level at the junction interface, and sufficient characteristics as a semiconductor light emission element cannot be brought out.
Such a semiconductor light emission element is also studied that a nitride semiconductor is formed on a dissimilar semiconductor substrate formed with inexpensive Si or GaAs, which is different from the sapphire substrate or the nitride semiconductor. However, two-step growth is carried out for growing the nitride semiconductor by using a buffer layer formed with GaN, AlN or ZnO, and therefore, the semiconductor substrate formed with the dissimilar semiconductor, such as Si and GaAs, functions only as a substrate to grow the nitride semiconductors but does not serve as a semiconductor light emission element. (Supratik Guha and Nestor A. Bojarczuk, Appl. Phys. Lett., vol. 72, p. 415 (1998), Chuong A. Tran, A. Osinski and R. F. Karlicek, Jr., Appl. Phys. Lett., vol. 75, p. 1494 (1999), and E. Feltin, S. Dalmasso, P. Mierry, B. Beaumont, H. Lahreche, A. Bouille, H. Haas, M. Leroux and P. Gibart, Jpn. J. Appl. Phys., vol. 40, L738 (2001))
While a heterogeneous junction between nitride semiconductors has been realized by a quantum well structure, the heterogeneous junction to the dissimilar semiconductor, such as Si and GaAs, is difficult to be formed as noted in the foregoing. Furthermore, there are such problems that the nitride semiconductor crystals are formed by providing a buffer layer, such as GaN, AlN and ZnO, at the interface to the dissimilar semiconductor, and the semiconductor junction cannot be directly formed.
As described in the foregoing, in the semiconductor light emission element having a constitution containing a nitride semiconductor layer and a dissimilar semiconductor (semiconductor substrate) different therefrom, the nitride semiconductor layer and the dissimilar semiconductor (semiconductor substrate) are formed through the buffer layer, such as GaN, AlN and ZnO, having insulating property, and the dissimilar semiconductor does not contribute to injection of charge (electrons or positive holes), whereby a large number of layers are required, and problems in cost are caused. Furthermore, in the case where the dissimilar semiconductor (semiconductor substrate) is shared by the other elements, and driving circuits and wiring from the other elements are formed on the semiconductor substrate in parallel with the semiconductor light emission element, the elements are not formed directly on the semiconductor substrate, and the semiconductor substrate does not electrically function by itself. As a result, there are problems of complex layer structure and high production cost, and it is the current situation that a composite element that has plural elements having different functions is difficult to be formed on the same semiconductor substrate.
The invention is to solve the foregoing problems associated with the conventional art to provide a simple and low cost semiconductor light emission element exerting high performance and a process for producing the same.
The invention is also to provide such a semiconductor light emission element capable of forming a semiconductor composite element that has plural semiconductor elements having different functions on the same dissimilar semiconductor (semiconductor substrate) and has high performance and a simple structure, and to provide the semiconductor composite element.
The invention provides, as one aspect, a semiconductor light emission element containing a nitride semiconductor layer at least containing one or more elements selected from Group IIIA elements and one or more elements selected from Group VA elements, a semiconductor having a polarity different from the nitride semiconductor layer and being dissimilar to the nitride semiconductor layer, and a light emission layer provided between the dissimilar semiconductor and the nitride semiconductor, wherein electrons or positive holes are injected from semiconductors of the dissimilar semiconductor and the nitride semiconductor layer to the light emission layer to carry out light emission.