JPS6327317B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field of the invention The present invention relates to an aluminum-gallium-arsenic compound that is placed in the atmosphere and has a natural oxide film on its surface, and an aluminum-gallium-arsenic compound that is lattice-matched to a single crystal of a gallium-arsenic compound. This invention relates to a molecular beam crystal growth method for growing single crystals. (b) Background of the Technology In semiconductor devices, particularly compound semiconductor devices, epitaxial growth in which a desired semiconductor crystal is grown in a lattice-matched manner to a semiconductor substrate crystal is widely practiced. In other words, semiconductor crystals obtained by epitaxial growth have a greater degree of freedom in selecting their forbidden band width, conductivity type, carrier concentration, thickness, etc., and are more susceptible to crystal defects and unintended impurity inclusions than substrate crystals. Epitaxial growth is also used to grow semiconductor layers with different compositions, and many of the semiconductor regions of optical semiconductor devices and the operating regions of field effect transistors are grown epitaxially. It is provided in the growth layer. (c) Prior art and problems Gallium-arsenide compounds (GaAs) and aluminum-gallium-arsenide compounds (AlxGa _1-x As) are best known as − group compound semiconductors, but AlxGa _1-x As crystals In order to achieve good lattice matching with GaAs crystal over a wide range _of aluminum (Al) composition ratio It is used in many semiconductor devices including effect transistors. As a method for epitaxially growing GaAs crystals or AlxGa _1-x As crystals, the molecular beam crystal growth method (hereinafter referred to as MBE method) is more sensitive to crystal composition ratio, impurity doping amount, or Since it is possible to accurately control the crystal growth rate and form steep crystal interfaces, it is most suitable for realizing the finest semiconductor crystal structure, such as a superlattice structure. A GaAs single crystal and an AlxGa _1-x As single crystal are epitaxially grown on a GaAs substrate crystal according to the required specifications by the MBE method, and this semiconductor substrate is once taken out into the atmosphere and then subjected to lithography or selective etching. GaAs or AlxGa _1-x
Epitaxial growth of As single crystals is often required in the manufacturing process of semiconductor devices. However, when GaAs and AlxGa _1-x As crystals come into contact with the atmosphere, there are usually 1 to 3
A natural oxide film having a thickness of about [nm] is formed. Therefore, once on the GaAs crystal surface that is in contact with the atmosphere,
When epitaxially growing GaAs or AlxGa _1-x As crystals, the natural oxide film is removed by heat treatment for about 1 minute at a temperature of 600 [°C] in the vacuum state of a conventional MBE equipment. M.B.E.
Growth is taking place. It is possible to remove the natural oxide film by this heat treatment at a temperature of about 600 [℃] for GaAs crystals as described above, but for AlxGa _1-x As crystals, it is possible to remove the natural oxide film by such a method. However, once the AlxGa _1-x As crystal surface is exposed to the atmosphere, GaAs or AlxGa _1-x with good surface morphology is
It is said that it is impossible to grow As single crystals, and this is a factor that restricts the structure or manufacturing process of semiconductor substrates. (d) Purpose of the Invention The present invention provides an AlxGa _{1-x As single crystal with a good surface morphology that is lattice matched to the AlxGa 1-x As} crystal and a GaAs crystal that is placed in the atmosphere and has a natural oxide film on its surface. An object of the present invention is to provide an epitaxial growth method for growing single crystals. (e) Structure of the invention According to the present invention, the above object
On the natural oxide film remaining on the surface of the gallium/arsenic compound single crystal, an aluminum/gallium/arsenic compound AlxGa _1-x As (however,
This is achieved by using a molecular beam crystal growth method that grows x=0.3). (f) Examples of the invention The present invention will be specifically explained below using examples. As a first embodiment of the present invention, as shown in the cross _- sectional view in FIG. , MBE Al _0.3 Ga _0.7 As layer 3
It grows to a thickness of about 50 to 500 [Å] by the method. However, the Al composition ratio x of the substrate single crystal 1 is 0.19,
0.3 and 0.46, and the MBE growth method uses Al _0.3 on the GaAs single crystal substrate surface where there is no native oxide film 2.
As in the Ga _0.7 As single crystal growth, the temperature of the substrate single crystal 1 was set, the Al _0.3 Ga _0.7 As single crystal growth rate was set to 1.5 [μm/h], and the background pressure of arsenic (As) was set to 1 × It is assumed to be around 10 ^-7 [Torr]. Al _0.3 Ga _0.7 As obtained by this MBE growth
The layer 3 is a single crystal in which the Al composition ratio x of the substrate single crystal 1 is matched to the substrate single crystal 1. The AlGaAs layer 3 was doped with 1×10 ¹⁸ cm ⁻³ of Si, and the CV measurement confirmed that the electron concentration was as set. Next, we measured the breakdown voltage (breakdown voltage) when Si-doped AlGaAs (X = 0.3, doping amount 1 x 10 ¹⁸ cm ^-3 ) was formed on AlGaAs with various X values, and the results are shown in the table below. show.

[Table] Note that when X=0, that is, when the gallium-arsenic compound was grown on the natural oxide film, the desired performance could not be obtained. Also, for X = 0.3, the above point has been clarified by experiment, but other
However, the value is unknown when grown on a native oxide film. As a second embodiment of the present description, as shown in the cross section of FIG. 2, an AlGaAs layer 12 of 5000 Å MBE is grown on a GaAs substrate 11, and after being exposed to the atmosphere, an AlGaAs layer 13 is grown to a thickness of d [Å ], grow only
Subsequently, a GaAs layer 14 was grown to a thickness of 2000 Å.
Samples were prepared with the thickness d of the AlGaAs layer 13 changed to three types: 0, 20, and 50 Å. When observed with the naked eye, those with d = 0 and 20 Å were in a cloudy state, but those with 50 Å were in a cloudy state. , the mirror surface was almost the same as the epitaxial state grown by normal MBE. In addition, when we took RHEED photos and replica photos of these samples and investigated them, we found that at d=0, there were many diamond-shaped depressions, which were spotty.
Many strong spots were seen in the RHEED photo. At d = 50 Å or more, the number of diamond-shaped depressions becomes extremely small, and the RHEED images also become streaky. If you plot the area occupied by the diamond-shaped depression from the replica photo into a graph with d on the horizontal axis, it will be 80 Å.
It is estimated that it will be less than 1%. (g) Effect of the invention As explained above, according to the present invention, AlxGa _1-x
The Alx′Ga _1-x′As compound single crystal was lattice-matched to the As compound single crystal by the MBE method without removing the natural oxide film formed in the atmosphere on the surface of the As compound single crystal. Furthermore, it is possible to grow a GaAs compound single crystal that is lattice-matched to the grown Alx′Ga _1-x′As compound single crystal. Therefore, according to the present invention, GaAs-AlxGa _1-x
When manufacturing As-based semiconductor devices, processing such as lithography or selective etching is performed in the atmosphere to expose the AlxGa _1-x As single crystal, which is difficult to remove the natural oxide film, or As a result, the AlxGa _1-x As single crystal is exposed, and after processing, Alx′Ga _1-x As is lattice-matched to this semiconductor.
Furthermore, the growth of GaAs single crystals can be carried out without conventional restrictions.

[Brief explanation of the drawing]

Figure 1 shows Al _0.3 Ga _0.7 on a single crystal AlxGa _1-x As substrate.
A cross-sectional view showing a first example of growing an As single crystal,
FIG. 2 is a sectional view showing a second embodiment in which a GaAs single crystal is grown on a GaAs single crystal substrate having AlxGa _1-x As via an AlxGa _1-x As single crystal. In the figure, 1 and 12 are single crystal AlxGa _1-x As substrates, 2 is a natural oxide film, and 3 and 13 are AlxGa 1-x As substrate single crystals.
AlxGa _1-x As single crystal, 14 indicates GaAs single crystal.

Claims (1)

[Claims] 1 On the natural oxide film remaining on the surface of the first aluminum/gallium/arsenic compound single crystal, a second aluminum/gallium/arsenic compound single crystal AlxGa ₁ -xAs (where X=
0.3) of 50 Å or more, and further growing a single crystal on the surface of the second aluminum/gallium/arsenic compound single crystal in the same vacuum.