JP2006216876A - Compound semiconductor epitaxial substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial substrate having a high electron mobility p-HEMT structure, and to provide a method for manufacturing it. <P>SOLUTION: When a compound semiconductor epitaxial substrate used for a high electron mobility field effect transistor, having an InGaAs layer as a channel layer 6 and an AlGaAs layer containing n-type impurities as electron supply layers 3 and 9 in an MOVPE method is manufactured, by using a triethyl gallium as a gallium raw material, the InGaAs layer is subjected to crystal-growing, under growing temperature conditions where the temperature of substrate is in a range of 450-490°C to make a channel layer 6 formed. Consequently, a HEMT manufacturing compound semiconductor epitaxial substrate of very high electron mobility is manufactured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a compound semiconductor epitaxial substrate for manufacturing a high electron mobility field effect transistor (hereinafter referred to as HEMT) and a manufacturing method thereof.

  HEMT, which is an element using a GaAs-based group 3-5 compound semiconductor, is used as a component of high-frequency communication equipment such as a mobile phone.

In this compound semiconductor epitaxial substrate for manufacturing HEMT, the temperature of a semi-insulating GaAs growth substrate is maintained at a temperature of about 550 to 700 ° C., a multilayer buffer layer made of GaAs and AlGaAs, and a channel made of InGaAs on the growth substrate. Metal organic vapor phase epitaxy (a spacer layer made of i-GaAs may be grown thereon and below), an electron supply layer (carrier layer) made of n-AlGaAs, and a contact layer made of n ⁺ -InGaAs ( The MOVPE method is used for sequential growth.

A compound semiconductor epitaxial substrate for HEMT manufacturing manufactured as described above is required to exhibit high electron mobility. As a method for producing the compound semiconductor epitaxial substrate exhibiting higher electron mobility than before, a production method for maintaining the temperature of the growth substrate at 550 ° C., which is lower than the conventional temperature, has been proposed, and high electron mobility of 3200 cm ² / V · s. The compound semiconductor epitaxial substrate which shows is obtained (for example, refer patent document 1). However, this value is not sufficient, and there has been a demand for a compound semiconductor epitaxial substrate and a method for producing the same, which exhibit higher electron mobility for HEMT production.
JP 2001-44127 A

  An object of the present invention is to provide a compound semiconductor epitaxial substrate and a method for manufacturing the same, which are used for HEMT manufacturing and exhibit higher electronic power than conventional ones.

  In order to solve the above-mentioned problems, the present inventors have intensively studied a method for producing a compound semiconductor epitaxial substrate for producing HEMT. As a result, the compound semiconductor epitaxial substrate for producing HEMT having an InGaAs layer as a channel layer is converted into MOVPE. A compound semiconductor for HEMT production that exhibits a higher electric power than the conventional one by using a specific compound as a starting material during crystal growth of the InGaAs layer and keeping the growth temperature within a predetermined range. The inventors have found that an epitaxial substrate can be manufactured and have completed the present invention.

  According to the first aspect of the present invention, a HEMT manufacturing compound is formed by sequentially growing a buffer layer, a channel layer made of InGaAs, an electron supply layer made of n-AlGaAs, and a contact layer on a growth substrate by metal organic vapor phase epitaxy. In a method for manufacturing a semiconductor epitaxial substrate, the InGaAs layer is grown using triethylgallium as a gallium raw material and the growth substrate temperature is in the range of 450 ° C. or higher and 490 ° C. or lower. A manufacturing method is proposed.

  According to invention of Claim 2, the compound semiconductor epitaxial substrate for HEMT manufacture manufactured by the method of Claim 1 is proposed.

According to the invention of claim 3, in claim 2, a compound semiconductor epitaxial substrate for manufacturing a HEMT having an electron mobility of 8500 cm ² / V · s or more is proposed.

  If the compound semiconductor epitaxial substrate manufactured according to the present invention is used, a HEMT having high electron mobility and good electrical characteristics can be manufactured.

  A method of manufacturing a compound semiconductor epitaxial substrate for HEMT manufacturing according to the present invention includes a buffer layer, a channel layer made of InGaAs, an electron supply layer made of n-AlGaAs on a semi-insulating GaAs growth substrate by metal organic vapor phase epitaxy. In the manufacturing method of sequentially growing contact layers, the InGaAs layer is grown using triethylgallium as a gallium source and the temperature of the growth substrate is in the range of 450 ° C. to 490 ° C.

  In the manufacturing method of the present invention, first, a growth substrate made of a high resistance semi-insulating GaAs single crystal or the like is prepared. As the growth substrate, a GaAs substrate manufactured by a LEC (Liquid Encapsulated Czochralski) method, a VB (Vertical Bridgman) method, a VGF (Vertical Gradient Freezing) method or the like is preferable, but not limited thereto. And even if it is the growth substrate manufactured by any method, the board | substrate which has the inclination of about 0.05 degrees-10 degrees from one crystallographic plane orientation is prepared.

  In order to remove foreign matter on the surface of the growth substrate, degreasing cleaning, etching, water washing, and drying treatment may be performed. Then, the growth substrate is placed on a heating stage of a known crystal growth furnace and heating is started. Prior to the start of heating, the inside of the furnace may be replaced with high-purity hydrogen or the like. When the temperature is stabilized at an appropriate temperature, an arsenic source gas is usually introduced into the growth furnace. For example, when a GaAs layer is grown as a buffer layer, a gallium source gas is subsequently introduced. Further, when growing a channel layer made of InGaAs, triethylgallium and indium source gases are introduced in addition to the introduction of the arsenic source gas. Further, when growing an electron supply layer made of n-AlGaAs, the gallium source gas, the aluminum source gas, and the n-type dopant source gas are introduced in addition to the introduction of the arsenic source gas. The buffer layer can be grown in the same manner. By controlling the supply amount and time of each raw material, desired compound semiconductor layers such as at least a buffer layer, a channel layer made of InGaAs, an electron supply layer made of n-AlGaAs, and a contact layer are sequentially grown on the growth substrate. To go.

  Here, in the manufacturing method of the present invention, when forming the channel layer, triethylgallium is used as the gallium source gas, the temperature of the GaAs single crystal substrate as the growth substrate is set in the range of 450 ° C. to 490 ° C., and InGaAs Form a layer. The thickness of this InGaAs layer is usually about 1 to 20 nm. Conventionally, the temperature of the growth substrate is about 600 ° C., and trimethylgallium is used as the gallium source gas. In this conventional case, if the growth substrate temperature is as low as 450 ° C. or higher and 490 ° C. or lower, the thermal decomposition of the gallium source gas is not sufficient, and the crystallinity of the InGaAs layer is lowered, so that it is used as a compound semiconductor substrate for HEMT. The electron mobility will fall to such an extent that it cannot be performed. However, by using triethylgallium as a gallium source gas and growing an InGaAs layer in a temperature range of 450 ° C. or more and 490 ° C. or less, the reason is not clear, but a compound semiconductor epitaxial substrate for HEMT manufacturing with extremely high electron mobility It is obtained.

  When a layer other than the InGaAs layer (channel layer) is grown, the growth substrate may be held in the range of 550 ° C. to 700 ° C. as in the conventional case.

  As the arsenic source gas, arsenic trihydride (arsine) is generally used in many cases, but alkylarsine in which hydrogen of arsine is substituted with an alkyl group having 1 to 4 carbon atoms can also be used. As the source gas for aluminum and indium, a trialkylate or trihydride in which an alkyl group having 1 to 3 carbon atoms or hydrogen is bonded to each metal atom is generally used.

  As the n-type dopant source gas, hydrides such as silicon, germanium, tin, sulfur, and selenium, or alkylates having an alkyl group having 1 to 3 carbon atoms can be used.

  After all layers are grown on the growth substrate in this way, the supply of each raw material is stopped to stop crystal growth, and after cooling, the stacked epitaxial substrate is taken out from the growth furnace to complete crystal growth. .

The compound semiconductor epitaxial substrate for HEMT production thus obtained shows higher electron mobility than the conventional one. Furthermore, there are cases where the electron mobility can be further increased by increasing the In content in the channel layer made of InGaAs or increasing the thickness of the channel layer. The electron mobility exhibited by the compound semiconductor epitaxial substrate for HEMT production according to the present invention produced as described above can be 8500 cm ² / V · s or more.

  An example of the structure of a compound semiconductor epitaxial substrate for HEMT production according to the present invention obtained by using the above-described method is shown as a layer structure diagram in FIG.

  In FIG. 1, reference numeral 1 denotes a growth substrate made of GaAs single crystal which is a single crystal substrate, and 2 denotes a buffer layer laminated on the growth substrate 1.

3 is a back-side electron supply layer formed as an n-Al _0.24 Ga _0.76 As layer having a thickness of 4 nm and doped with an n-type impurity of 3 × 10 ¹⁸ / cm ^3. The back side spacer layers 4 and 5 are laminated in this order. Here, the back side spacer layer 4 is a 3 nm thick i-Al _0.24 Ga _0.76 As layer, and the back side spacer layer 5 is a 4 nm thick i-GaAs layer. Reference numeral 6 denotes a channel layer in which a two-dimensional electron gas for flowing two-dimensional electrons is formed, and is composed of an i-In _0.30 Ga _0.70 As layer having a thickness of 7.5 nm.

Reference numerals 7 and 8 each denote a front spacer layer, the front spacer layer 7 is a 4 nm thick i-GaAs layer, and the front spacer layer 8 is a 3 nm thick i-Al _0.24 Ga _0.76 As layer.

_{Reference numeral} 9 denotes a front-side electron supply layer, which is formed as an n-Al _0.24 Ga _0.76 As layer having a thickness of 10 nm, and is doped with n-type impurities at a concentration of 3 × 10 ¹⁸ / cm ³ . Reference numerals 10 and 11 denote undoped layers, which are stacked as an i-Al _0.22 Ga _0.78 As layer having a thickness of 5 nm and an i-GaAs layer having a thickness of 20 nm, respectively.

  Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to these Examples.

Example 1
A compound semiconductor epitaxial substrate for HEMT production having the layer structure shown in FIG. 1 was prepared as follows using a reactor for a reduced pressure barrel type MOVPE method. A semi-insulating GaAs single crystal plate manufactured by the VGF method was prepared, and this was used as a growth substrate 1, and each layer was epitaxially grown thereon. Triethylgallium (TEG), trimethylaluminum (TMA), and trimethylindium (TMI) were used as Group ₃ materials, and arsine (AsH ₃ ) was used as Group 5 materials. Silicon (Si) was used as the n-type dopant. As a raw material carrier gas, high-purity hydrogen was used, and epitaxial growth was performed under growth conditions of a reactor pressure of 0.1 atm and a growth rate of 3 to 1 μm / hr. Here, the growth temperature conditions were a growth substrate temperature of 490 ° C. when the channel layer 6 was grown and 650 ° C. when a layer other than the channel layer 6 was grown.

  As shown in FIG. 1, the In composition of the channel layer 6 for running electrons was 0.30, and the film thickness was 7.5 nm. On the upper and lower sides of the i-InGaAs layer used for the channel layer 6, the i-GaAs layers as the spacer layers 6 and 8 were epitaxially grown by 4.0 nm on the upper and lower sides, respectively.

As a result of hole measurement by the Van der Pauw method in the epitaxial substrate obtained by manufacturing as described above, the two-dimensional electron gas concentration at room temperature (300 K) is 2.40 × 10 ¹² / cm ² , room temperature. The electron mobility at (300 K) is 8840 cm ² / V · s, the two-dimensional electron gas concentration at 77 K is 2.65 × 10 ¹² / cm ² , and the electron mobility at 77 K is as high as 39300 cm ² / V · s. Got the value.

(Comparative Example 1)
An epitaxial substrate having the layer structure shown in FIG. 1 was produced in the same manner as in Example 1 except that the channel layer 6 was formed at 520 ° C. As a result of measuring the Hall in the same manner as in Example 1, the two-dimensional electron gas concentration at room temperature (300 K) is 2.40 × 10 ¹² / cm ² , and the electron mobility at room temperature (300 K) is 8240 cm ² / V. The two-dimensional electron gas concentration at s and 77K was 2.65 × 10 ¹² / cm ² , and the electron mobility at 77K was 28000 cm ² / V · s.

(Comparative Example 2)
An epitaxial substrate having the layer structure shown in FIG. 1 was produced in the same manner as in Example 1 except that the channel layer 6 was formed at a temperature of 550.degree. As a result of performing the hole measurement in the same manner as in Example 1, the two-dimensional electron gas concentration at room temperature (300 K) was 2.32 × 10 ¹² / cm ² , and the electron mobility at room temperature (300 K) was 8070 cm ² / V. The two-dimensional electron gas concentration at s and 77K was 2.54 × 10 ¹² / cm ² , and the electron mobility at 77K was 27200 cm ² / V · s.

(Comparative Example 3)
An epitaxial substrate having the layer structure shown in FIG. 1 was produced in the same manner as in Example 1 except that the channel layer 6 was formed at a temperature of 580 ° C. As a result of performing the hole measurement in the same manner as in Example 1, the two-dimensional electron gas concentration at room temperature (300 K) was 2.40 × 10 ¹² / cm ² , and the electron mobility at room temperature (300 K) was 7980 cm ² / V. The two-dimensional electron gas concentration at s and 77K was 2.62 × 10 ¹² / cm ² , and the electron mobility at 77K was 25000 cm ² / V · s.

  FIG. 2 is a graph showing the relationship between the substrate temperature during the growth of the channel layer 6 in Example 1 and Comparative Examples 1 to 3 and the electron mobility at room temperature (300K) and 77K.

The layer structure figure of one Embodiment of the compound semiconductor epitaxial substrate by this invention. The graph which shows the relationship between the growth substrate temperature based on each measurement result of the Example of this invention, and the electron mobility of a channel layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Growth substrate 2 Buffer layer 3 Back side electron supply layer 4, 5 Back side spacer layer 6 Channel layer 7, 8 Front side spacer layer 9 Front side electron supply layer 10, 11 Undoped layer

Claims (3)

  In the method of manufacturing a compound semiconductor epitaxial substrate for manufacturing HEMT, a buffer layer, a channel layer made of InGaAs, an electron supply layer made of n-AlGaAs, and a contact layer are sequentially grown on a growth substrate by metal organic vapor phase epitaxy. A method of manufacturing a compound semiconductor epitaxial substrate for HEMT manufacturing, wherein an InGaAs layer is grown using triethylgallium as a gallium source and the temperature of the growth substrate is in the range of 450 ° C. or higher and 490 ° C. or lower.   A compound semiconductor epitaxial substrate for HEMT manufacturing manufactured by the method of claim 1.   3. The compound semiconductor epitaxial substrate for manufacturing HEMT according to claim 2, wherein the electron mobility is 8500 cm <2> /V.s or more.

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