Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-09-13
2003-10-28
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S603000, C438S606000, C257S043000
Reexamination Certificate
active
06638846
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of growing a p-type ZnO based oxide semiconductor layer in which a p-type ZnO based oxide semiconductor layer is grown with a high carrier concentration and a method of manufacturing a semiconductor light emitting device using the same. More specifically, the present invention relates to a method of growing a p-type ZnO based oxide semiconductor layer in which the acceptor level of a p-type dopant is reduced and p-type dopants are doped to fully act as acceptors, thereby sufficiently increasing a carrier concentration thereof and a method of manufacturing a semiconductor light emitting device using the same.
BACKGROUND OF THE INVENTION
A blue color based (a wavelength region from ultraviolet to yellow) light emitting diode (hereinafter referred to as an LED) to be used for a full color display, a signal light or the like and a blue laser diode (hereinafter referred to as an LD) for a very fine DVD light source for a next generation which continuously oscillates at a room temperature can be obtained by laminating GaN based compound semiconductor layers on a sapphire substrate and have recently attracted the attention. While the GaN based compound semiconductor is in major in the light emitting device having a short wavelength, it has also been investigated that a II-VI compound semiconductor such as ZnO is used. The ZnO has a band gap of 3.37 eV at a room temperature and it has also been expected that the ZnO based oxide can be applied to a transparent conductive film, a transparent TFT and the like in addition to the DVD light source.
In ZnSe, a p-type semiconductor layer to be the II-VI compound has been implemented by activating a nitrogen gas using a plasma and doping the activated nitrogen. However, the same method has been tried for the ZnO and a p-type layer having a high carrier concentration has not been implemented. For example, it is apparent that an N concentration obtained by SIMS when growing a ZnO layer while supplying a ZnO material and plasma nitrogen to be a p-type dopant at a high substrate temperature of 500 to 60° C. is very small like a noise as shown in
FIG. 9
together with a secondary ion strength of ZnO. In
FIG. 9
, there is a portion in which the N concentration has a maximum value based on the fact that a substrate is once taken out of a growing apparatus in order to grow an undoped ZnO layer and an N-doped p-type layer and to recognize a boundary thereof. However, it is apparent that the N concentration is rarely varied between the undoped layer and the p-type layer. The reason why the N concentration is very noisy in
FIG. 9
is that a concentration is low and close to the limit of the measurement based on the SIMS.
Although the reason is not definite, for example, it has been published that nitrogen entering an oxygen site of ZnO (the condition of p-type conduction) creates a deep acceptor level of approximately 200 meV, and furthermore, makes crystal structure unstable and generates an oxygen hole so that doping of ZnO with nitrogen becomes hard in “Solution using a codoping method to Unipolarity for the fabrication of p-type ZnO” (Japanese Journal of Applied Physics, Vol. 38, pp. 166 to 169, 1999) written by T. Yamamoto et al. As one of the solutions, the paper has proposed a codoping method for simultaneously doping nitrogen to be an acceptor and a III group element to be a donor. More specifically, there have been described the effect of mutually bonding a III group element and nitrogen through codoping to enter into a ZnO crystal lattice, thereby preventing the instability of crystals from being caused by nitrogen doping and the effect of reducing the acceptor level.
As described above, it has been proposed that a III group element such as Ga to be an n-type dopant is simultaneously doped in addition to nitrogen to be a p-type dopant in order to form the p-type ZnO based oxide semiconductor layer. However, there is a problem in that a p-type layer having a high carrier concentration cannot be obtained even if the nitrogen and the III group element such as Ga are actually doped simultaneously. In particular, although the present inventors have found that a residual carrier concentration is reduced when a ZnO based oxide is grown at a high temperature of 500° C. or more, during a high temperature epitaxial growth, particularly, an oxidation speed is higher than a nitrogenization speed. Therefore, there is a problem in that Ga is more doped than main N even if the simultaneous doping is carried out, as shown in
FIGS. 7 and 8
showing the concentrations of Ga and N obtained by the simultaneous doping at 600° C.
FIG. 7
shows that a larger amount of Ga is doped than that in
FIG. 8 and N
is also doped more easily if the amount of Ga to be doped is increased. However, the concentration of N does not exceed that of Ga.
SUMMARY OF THE INVENTION
In consideration of the circumstances, it is an object of the present invention to provide a method of growing a p-type ZnO based oxide semiconductor layer capable of doping N to be a p-type dopant at a stable carrier concentration and sufficiently increasing the carrier concentration of the p-type layer made of ZnO based oxide semiconductor, by employing a simultaneous doping method in high temperature growth in which a residual carrier concentration can be reduced.
It is another object of the present invention to provide a method of manufacturing a semiconductor light emitting device which can grow a p-type ZnO based oxide semiconductor layer having a high carrier concentration, thereby obtaining a semiconductor light emitting device such as a light emitting diode or a laser diode which is excellent in a light emitting efficiency.
The present inventors investigated to solve the reason why a p-type ZnO based oxide semiconductor layer having a sufficiently high carrier concentration cannot be obtained by codoping. As a result it was found that the chemical activity of oxygen is very high on the condition that Zn, O, N to be a p-type dopant and Ga to be an n-type dopant coexist and grow, for example, so that a reaction of ZnO and GaO is caused much more early than that of ZnN and GaN.
In other words, the following is apparent from the theory of the above-mentioned paper. Even if N alone enters into the site of O of a ZnO crystalline structure, the crystalline structure becomes unstable or an acceptor level becomes too deep, which is not preferable. By doping Ga, a Ga-N bond is formed and if the amount of N becomes larger than that of Ga, the doped N can effectively act as an acceptor with an —N—Ga—N— bond. However, even if N and Ga are simply supplied, the reaction of ZnO and GaO proceeds early so that the —N—Ga—N— bond cannot be obtained and Ga is replaced with Zn to obtain an —O—Zn—O—Ga—O— structure and to act as an n-type dopant. Therefore, the p-type layer is adversely affected.
The present inventors found that at least the supply of an O material is stopped to carry out the doping when supplying a Ga material so that an —N—Ga—N— bond is obtained and is further combined with O of a ZnO semiconductor layer and N is bonded to Ga with a bond of —O—Zn—N—Ga—N—Zn—O— so that a p-type ZnO semiconductor layer acting as an effective acceptor can be obtained.
The present invention provides a method of growing a p-type ZnO based oxide semiconductor layer wherein when a p-type dopant material made of N and an n-type dopant material are to be simultaneously supplied to grow the p-type ZnO based oxide semiconductor layer, at least the supply of O in raw materials constituting a ZnO based oxide is stopped when supplying the n-type dopant material, and thereby carrying out growth.
The ZnO based oxide semiconductor means an oxide containing Zn, and specifically includes an oxide of IIA group and Zn, IIB group and Zn or IIA and IIB groups and Zn in addition to ZnO, respectively.
By using the method, as described above, the bond of Zn or the III group element and O is suppressed and the bond of N to be the p-type dopant and the III group element such as Ga
Fons Paul
Iwata Kakuya
Matsubara Koji
Nakahara Ken
Niki Shigeru
Arent Fox Kintner Plotkin & Kahn
Lee Calvin
National Institute of Advanced Industrial Science and Technology
Smith Matthew
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