JP3972090B2 - Thin film growth method - Google Patents

Description

【００１７】
【発明の効果】
本願発明によれば、以下のような効果を奏することができる。
（１）本願発明により、III-V族化合物上に成長させたII-VI族化合物薄膜の欠陥密度を減少させて良質な結晶を得ることができる。
（２）本願発明により、III-V族化合物上に光損失の少ないII-VI族化合物からなる半導体磁気光学導波路を得ることができる。
（３）本願発明により、III-V族化合物上に寿命の長いII-VI族化合物からなる半導体レーザダイオードを得ることができる。
【図面の簡単な説明】
【図１】 本願発明による成長方法を模式的に説明するものであり、III-V族化合物上へのII-VI族化合物薄膜の成長を示している。
【図２】反射型高速電子線回折（RHEED)のスペキュラー回折の強度とGaAs基板上に堆積させたZn元素からなるアモルファス薄膜の厚みの関係を示したものである。
【図３】アモルファスZn薄膜の蒸発プロセス中の反射型高速電子線回折（RHEED)のスペキュラー回折の強度を、時間の関数として示したものである。図２の校正データを用いて評価したアモルファスZn薄膜の膜厚も示す。
【図４】本願発明の方法を用いGaAs基板上に成長させたCd₁-xMnxTe磁気光学導波路の構造を表す模式図である。
【符号の説明】
１ III−Ｖ族化合物
２ 厚みが０．６ｎｍ以上あるII族元素
３ 厚みが０．１〜０．６ｎｍのII族元素アモルファス薄膜
４ II−ＶI族化合物薄膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the growth of thin films, and particularly to the growth of II-VI group semiconductor thin films, and relates to Cd _1-x Mn _x Te magneto-optic waveguides, ZnSe laser diodes, and CdTe infrared detectors.
[0002]
[Prior art]
II-VI semiconductor thin films grown on III-V semiconductor substrates are applied to many important devices such as Cd _1-x Mn _x Te magneto-optic waveguides, ZnSe laser diodes, and CdTe infrared detectors. Is done. For the good operation of these devices, reducing the defect density of the crystal is very important. Degradation of ZnSe-LEDs on GaAs substrates is caused by a sharp decrease in active layer gain due to increased defects and increased non-radiative recombination. (A.Ishibashi, J.Cryst. Growth 159 (1996) 555). Defect spreading in Cd _1-x Mn _x Te waveguides causes light loss through increased light scattering and light absorption (W. Zaets and K. Ando, Appl. Phys. Lett. 77 (2000) 1593).
In epitaxial growth of II-VI thin films on III-V substrates, surface treatment of the substrate and crystal growth conditions at the initial stage of growth are very important for realizing a low defect density. In epitaxial growth of ZnSe thin films on GaAs substrates, there is a method in which (001) -oriented GaAs is homoepitaxially grown, and Zn is exposed to the (2x4) surface rearranged As termination surface, and then the ZnSe thin film is grown by migration epitaxy. Has been widely adopted as an effective method to minimize the stacking fault density (JM DePuydt et.al.US patent 5,879,962 and LH Kuo, L. Salamanca-Riba, BJWu, G.Hofler, JMDePuydt, H.Chen , Appl. Phys. Lett. 67 (1995) 3298).
Exposure to Group II elements such as Zn and Cd prevents the III-V substrate from reacting with Group VI elements such as Se and Te in the early stages of II-VI thin film growth (LHKuo, K. Kimura, A. Ohtake, S. Miwa, T. Yasuda, and T. Yao, J. Vac. Sci., Technol. B 15 (1997) 1241 and JM DePuydt et.al. US patent 5,879,962). However, it is known that the ratio of the surface of the GaAs substrate covered with Zn is low when exposed to group II elements (S. Miwa et.al. Appl. Phys. Lett. 73 (1998) 939). Therefore, group VI elements (Se and Te) still react with the GaAs substrate.
[0003]
[Problems to be solved by the invention]
Conventionally, when a II-VI compound thin film is grown on a III-V compound, in the initial stage, a VI group element reacts with a III-V compound to form a compound (Group III) ₂ (Group VI) ₃ This has resulted in high density defects in the thin film, causing degradation of the performance of the fabricated device.
[0004]
[Means for Solving the Problems]
The present invention solves this problem by covering the surface of a group III-V compound with an amorphous thin film made of a group II material before the growth of the group II-VI compound. As a result, it is possible to reduce the optical loss of the II-VI semiconductor optical waveguide provided on the III-V semiconductor substrate and to extend the life of the II-VI semiconductor laser.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a thin film growth apparatus including a source that generates a flux of at least one group II element and a source that generates a flux of at least one group VI element is used. The group II-element amorphous thin film is grown by adjusting the temperature of the group III-V compound placed in the thin film growth apparatus to the temperature at which the group II element amorphous thin film grows. Thereafter, the substrate is heated to a temperature suitable for the growth of the II-VI group thin film and the group II element amorphous thin film evaporating. When the Group II element amorphous thin film evaporates and its thickness falls within the range of 0.1 nm to 0.6 nm, the Group II element flux and the Group VI element flux are supplied in the same way, and The II-VI group thin film is grown.
[0006]
The present invention includes monitoring the thickness of the amorphous thin film using the intensity of the diffraction pattern of reflection high-energy electron diffraction. Electron diffraction is caused by using an electron beam accelerated by a high voltage, and the intensity of the diffraction pattern is detected by a photodetector such as a CCD camera. The thickness of the amorphous thin film can be known using the relationship between the intensity of the diffraction pattern and the thickness of the amorphous thin film, which has been calibrated in advance.
[0007]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 schematically illustrates the growth method according to the present invention, and shows the growth of a II-VI group compound thin film on a III-V group compound. White circles in the figure represent Group II elements, and black circles represent Group VI elements.
[0008]
Number 1 is a Group III-V compound, Number 2 is a Group II element amorphous thin film having a thickness of 0.6 nm or more, Number 3 is a Group II element amorphous thin film having a thickness between 0.1 nm and 0.6 nm, and Number 4 is II-VI group compound thin film.
[0009]
FIG. 1a) is the first stage of the growth method according to the invention. Supply the group II element flux to the surface of the group III-V compound. When the temperature of the substrate is adjusted (30 ° C. to 75 ° C.) so that a group II element amorphous thin film is formed, a group II element amorphous thin film grows on the group III-V compound.
[0010]
FIG. 1b) is the second stage of the growth method according to the invention. The sample is heated to a temperature (180 ° C. to 250 ° C.) suitable for the growth of the II-VI group compound thin film and the group II element amorphous thin film evaporating. Wait until the group II element amorphous thin film evaporates and its thickness falls within the range of 0.1 nm to 0.6 nm.
[0011]
FIG. 1c) is the third stage of the growth method according to the invention. When the Group II element amorphous thin film evaporates and the thickness falls within the range of 0.1 nm to 0.6 nm, the Group II element flux and the Group VI element flux are supplied in the same manner.
[0012]
FIG. 1d) is the third stage of the growth method according to the invention. A II-VI compound thin film grows on the III-V compound. After the II-VI group compound was grown from one atomic layer to two atomic layers, the growth was stopped and the sample temperature was raised from 300 ° C. to 350 ° C. and held for 1 minute or longer. This heat treatment process is necessary in order not to leave an excessive group II element at the interface between the group III-V compound and the group II-VI compound. When this heat treatment process was not performed, defects were observed on the produced thin film surface with a microscope. This defect did not occur when the heat treatment process was performed.
[0013]
FIG. 2 shows an amorphous structure made of Zn deposited on a GaAs substrate, which is a III-V group compound having a (001) orientation, in which the intensity of specular diffraction in reflection high-energy electron diffraction (RHEED) is maintained at 70 ° C. It is shown as a function of the thickness of the thin film. This corresponds to the stage of FIG. 1a), which is the first stage of growth. There is a clear correspondence between the diffraction intensity and the thickness of the amorphous thin film. This relationship can be used to know the thickness of the amorphous thin film during the growth process.
[0014]
FIG. 3 shows the intensity of specular diffraction of reflection high-energy electron diffraction (RHEED) during the evaporation process of an amorphous Zn thin film as a function of time when the sample temperature is 220 ° C. This corresponds to the stage of FIG. 1b), which is the second stage of growth. The thickness of the amorphous Zn thin film evaluated using the calibration data of FIG. 2 is also shown in FIG. From FIG. 3, the thickness of the amorphous thin film becomes a value between 0.1 nm and 0.6 nm, and the timing corresponding to the stage of FIG. 1c), which is the third stage of growth, can be determined correctly.
[0015]
FIG. 4 is a schematic diagram showing the structure of a Cd _1-x Mn _x Te magneto-optic waveguide grown on a GaAs substrate using this method. First, a ZnTe thin film was grown on a GaAs substrate by the method shown in FIG. 1, and a CdTe thin film and two Cd _1-x Mn _x Te layers were grown thereon. A Cd _0.7 Mn _0.3 Te cladding layer is provided under the Cd _0.85 Mn _0.15 Te core layer that functions as an optical waveguide layer.
[0016]
In order to demonstrate the effectiveness of the present invention, the X-ray diffraction parameter and the amount of light propagation loss, which are proportional to the amount of defects, were compared with those grown with and without applying this method. . The results are shown in Table 1. This is the case where ZnTe is grown directly on a GaAs substrate, the case where ZnTe is grown after using the conventional method of exposing the surface of the GaAs substrate to a Zn beam, and the case of growth by the method of the present invention. As can be clearly seen from the table, the width of the X-ray diffraction peak, the X-ray coherent length, the twin density, and the light propagation loss all show the superiority of the present invention.
[Table 1]

[0017]
【The invention's effect】
According to the present invention, the following effects can be obtained.
(1) According to the present invention, a high-quality crystal can be obtained by reducing the defect density of the II-VI group compound thin film grown on the III-V group compound.
(2) According to the present invention, a semiconductor magneto-optic waveguide composed of a II-VI group compound with little optical loss can be obtained on a III-V group compound.
(3) According to the present invention, it is possible to obtain a semiconductor laser diode composed of a II-VI group compound having a long lifetime on a III-V group compound.
[Brief description of the drawings]
FIG. 1 schematically illustrates a growth method according to the present invention, and illustrates the growth of a II-VI group compound thin film on a III-V group compound.
FIG. 2 shows the relationship between the intensity of specular diffraction in reflection high-energy electron diffraction (RHEED) and the thickness of an amorphous thin film made of Zn deposited on a GaAs substrate.
FIG. 3 shows the intensity of specular diffraction of reflection high-energy electron diffraction (RHEED) during the evaporation process of an amorphous Zn thin film as a function of time. The film thickness of the amorphous Zn thin film evaluated using the calibration data of FIG. 2 is also shown.
FIG. 4 is a schematic diagram showing the structure of a Cd ₁ -xMnxTe magneto-optic waveguide grown on a GaAs substrate using the method of the present invention.
[Explanation of symbols]
1 Group III-V compound 2 Group II element having a thickness of 0.6 nm or more 3 Group II element amorphous thin film having a thickness of 0.1 to 0.6 nm 4 Group II-VI compound thin film

Claims (5)

In a thin film growth method in which a II-VI group compound is laminated on a III-V compound, a group VI element constituting the II-VI group compound reacts with a group III element constituting the III -V compound. In order to prevent the formation of a compound different from the II-VI group compound, the surface of the III-V compound is protected with an amorphous film composed of a Group II element not containing a Group VI element , The amorphous film is evaporated by raising the temperature, and the growth of the II-VI group compound is started when the thickness of the group II element falls within the range of 0.1 nm to 0.6 nm. Method. The group II element is Zn or Cd, the group VI element is Te, Se or S, the temperature of the sample when forming the amorphous layer is 30 ° C to 75 ° C, and the amorphous layer is 180 ° C The thin film growth method according to claim 1 , wherein the film is evaporated at a temperature of about 250 to 250 ° C. After the evaporation, the II-VI group compound is grown in one or two atomic layers, the growth is temporarily stopped, the sample temperature is raised from 300 ° C. to 350 ° C. and held for 1 minute or more, and then the sample is again 4. The method of growing a thin film according to claim 3, wherein the temperature is lowered between 180 ° C. and 250 ° C. to resume the growth of the II-VI group compound. The group III-V compound GaAs, InP, thin film growth method of claim 1, wherein it is InSb or GaSb. Measure the thickness of the group II material using the information on the reflection pattern intensity of reflection high-speed electron diffraction in the step of supplying the group II material flux onto the group III-V semiconductor substrate and the step of evaporating the group II material. A thickness monitoring method characterized by:

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