WO2017094028A1

WO2017094028A1 - Method and apparatus for forming silicon doped gallium nitride (gan) films by a co-sputtering technique

Info

Publication number: WO2017094028A1
Application number: PCT/IN2016/050428
Authority: WO
Inventors: Shyam Mohan; Syed Salahuddin MAJOR; Raman S SRINIVASA; Qazi Zahid HUSAIN
Original assignee: Indian Institute Of Technology Bombay
Priority date: 2015-12-02
Filing date: 2016-12-01
Publication date: 2017-06-08

Abstract

An apparatus (100a, 100b, 100c) and a method for forming silicon doped GaN films by a co-sputtering of Si (104b) and GaAs (104a), with an argon-nitrogen gas mixture. The method comprising: forming Si doped GaN films in response to an interaction between argon-nitrogen gas mixture with Si (104b) and GaAs (104a).

Description

"Method and apparatus for forming silicon doped Gallium Nitride (GaN) films by a co-sputtering technique"

FIELD OF INVENTION

[0001] The embodiments herein relate to deposition of Gallium Nitride (GaN) films on a substrate and more particularly relates to a method for forming silicon doped Gallium Nitride (GaN) films. The present application is based on, and claims priority from an Indian Application Number 4554/MUM/2015 filed on 2^nd December, 2015 the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF INVENTION

[0002] Single crystal Gallium Nitride (GaN) is an important material finding increasing use in Radio Frequency (RF) devices, and Light Emitting Diodes (LEDs). The interest in GaN has been accelerated by the development, demonstration and even commercialization of nitride based devices such as light emitters and Metal- Semiconductor Field Effect Transistors (MESFETs) which allow operation in adverse operating conditions such as higher temperatures. However, parasitic contact resistance significantly reduce the performance of various electronic devices. Hence, minimization of contact resistance is of importance. While, heavy doping of contact layers allow low contact resistance, wide gap semiconductors such as nitrides offer more challenges and limit the doping. Thus, an essential element in fabrication of GaN based electronic devices is the development of Silicon (Si) doped GaN films, with moderately (n-type) to heavy (n⁺-type) doping.

[0003] Generally, the growth of Si doped GaN films are carried out by Metal Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE). The doping of GaN with the Si is also implemented by ion implantation. The Si implanted into GaN requires annealing at approximately 1100°C for activation and 100 % substitution. The growth of Si doped GaN films with MOCVD requires growth temperatures greater than 1000°C. The carrier concentration of Si doped GaN films by MOCVD are found in the range of 10 1¹8⁰ cm -^"3³ to 101"9 cm -3.

[0004] The growth of Si doped GaN films by the MBE requires relatively lower temperatures in the range of 600 °C to 900 °C. The carrier concentration of Si doped GaN films grown by a plasma assisted-MBE and a radio frequency-MBE are typically in the range of 10 19 cm -^"3 to 1020 cm -^"3.

Although high doping levels can be achieved with the MBE at relatively lower temperatures, the limitations of scalability and substrate size limits the application of the MBE to a large extent.

[0005] The above information is presented as background information only to help the reader to understand the present invention.

Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.

OBJECT OF INVENTION

[0006] The principal object of the embodiments herein is to provide a method for forming silicon (Si) doped Gallium Nitride (GaN) films by a co-sputtering of Si and Gallium Arsenide (GaAs), with an argon -nitrogen gas mixture.

[0007] Another object of the embodiments herein is to provide a method for placing Si on the GaAs for forming the Si doped GaN films.

[0008] Another object of the embodiments herein is to provide a method for placing Si and GaAs separately for forming the Si doped GaN films.

SUMMARY

[0009] Accordingly the embodiments herein provide a method for forming Si doped GaN films by a co-sputtering of Si and Gallium Arsenide (GaAs), with an argon-nitrogen gas mixture. The method includes forming Si doped GaN films in response to the interaction between the argon- nitrogen gas mixture with the Si and the GaAs.

[0010] Accordingly the embodiments herein provide an apparatus. The apparatus includes a vacuum chamber with a gas inlet. The vacuum chamber includes substrate and target(s). The substrate and the target materials are placed at a distance. Silicon (Si) and Gallium Arsenide (GaAs) targets are placed in the vacuum chamber. Argon and nitrogen gases are passed through the inlet and ionized to interact with the Si and the GaAs. A Si doped GaN film is formed in response to the interaction.

[0011] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0012] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0013] FIG. 1A shows an apparatus in which a silicon (Si) is placed on a Gallium Arsenide (GaAs) to form Si doped GaN film by co-sputtering of the Si and the GaAs, according to the embodiments as disclosed herein; [0014] FIG. IB shows the apparatus in which the Si and GaAs are placed separately to form Si doped GaN film by co-sputtering of the Si and the GaAs, according to the embodiments as disclosed herein;

[0015] FIG. 1C shows an apparatus in which the Si doped GaN film is formed by co-sputtering of the Si and the Gallium Arsenide (GaAs), where a gas inlet is present external to the apparatus, according to the embodiments as disclosed herein; and

[0016] FIG. 2 is a flow chart illustrating a method for forming the silicon doped GaN films, according to the embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION

[0017] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well- known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a nonexclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0018] Prior to describing the embodiments in detail, it is useful to provide details related to basic sputtering technique for better understanding of the embodiments provided in this disclosure.

[0019] Generally, to deposit a thin film on a substrate by sputtering of a target, the following steps are required. First, the substrate and the target are placed in a chamber. Then, the chamber is vacuumized or evacuated. A sputtering gas is introduced into the vacuumized chamber and ionized and accelerated to bombard the target. The target is caused to sputter and deposit the thin film on the substrate by the bombardment of the ionized sputtering gas. After the sputtering deposition, the substrate is taken out of the chamber. As such, the chamber needs to be vacuumized prior to each instance of sputtering deposition, reducing convenience and efficiency while increasing costs. [0020] The embodiments herein achieve a method for forming silicon Si doped GaN films by a co- sputtering of Si and Gallium Arsenide (GaAs), with an argon-nitrogen gas mixture. The method includes forming Si doped GaN films in response to the interaction between the ionized argon-nitrogen gas mixture with the Si and the GaAs.

[0021] In an embodiment, the Si is placed on the GaAs. In an embodiment, the Si and GaAs are placed separately.

[0022] In an embodiment, a co-sputtering ratio of Si 104b to the GaAs 104a is varied by varying the size of Si 104b and argon gas to nitrogen gas ratio to form the Si doped GaN films of different doping levels.

[0023] The embodiments herein provide an apparatus in which the Si doped GaN film is formed by co-sputtering of the Si and the Gallium Arsenide (GaAs).

[0024] Unlike the conventional methods, the proposed method can be used to form the Si doped GaN films by co-sputtering of the Si and the Gallium Arsenide (GaAs), with the argon-nitrogen gas mixture. The proposed method can be used to increase doping level of the Si in the GaN over a wide range of carrier concentrations. With the proposed method, using targets as Si and GaAs, when the argon-nitrogen gas is passed on to the target, the argon-nitrogen gas interacts with the GaAs and the Si to form the Si doped GaN films on the substrate.

[0025] Referring now to the drawings and more particularly to FIGS. 1A, IB, 1C and 2 where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0026] FIG. 1A shows an apparatus in which silicon (Si) doped Gallium Nitride (GaN) film is formed by co-sputtering of the Si and the Gallium Arsenide (GaAs), according to the embodiments as disclosed herein. As depicted in the FIG. 1A, the apparatus 100a includes a vacuum chamber 102a, a target 104a, target 104b, a substrate 106a and a gas inlet 108a.

[0027] In an embodiment, the target 104a is Gallium Arsenide (GaAs) and the target 104b is Si, as shown in the FIG. 1A.

[0028] In an embodiment, a method for forming Si doped GaN films is as described herein. Initially, the chamber 102a is evacuated before forming the Si doped GaN film on the substrate 106a. In an embodiment, the chamber 102a is evacuated to approximately 10^"6 mbar and filled with argon-nitrogen gas mixture to a pressure of approximately 10^" mbar before forming the Si doped GaN films on the substrate 106a.

[0029] The Si 104b is placed on the GaAs 104a. In an embodiment, the Si 104b is placed on the GaAs 104a to co-sputter the Si 104b and GaAs 104a. In an embodiment, the co-sputtering ratio of Si 104b and the GaAs 104a is varied by varying the percentage of area coverage of the GaAs 104a erosion track with the Si 104b. It should be noted that the variation of the Si area coverage from 2 - 20 % is found to result in a change of carrier concentration of the GaN films deposited on the substrate 106a.

[0030] The sputtering gas which includes argon-nitrogen is passed on to the Si 104b and GaAs 104a through the gas inlet 108a. In an embodiment, the percentage of nitrogen in the sputtering gas is varied from 10 to 100% and the temperature in the chamber 102a is varied from room temperature to approximately 700 °C.

[0031] When the argon-nitrogen gas is passed on to the Si 104b and the GaAs 104a, argon-nitrogen gas sputters the Si 104b and the GaAs 104a. When the ionized nitrogen gas reacts with the sputtered GaAs, Si doped GaN film is formed on the substrate 106a.

[0032] It should be noted that the Si doped GaN films are deposited as Si doped GaN layer on the substrate 106a when the argon-nitrogen gas interacts with the Si and the GaAs. Further, the GaN films are annealed at a temperature of 700 °C in nitrogen at a pressure on 8 x 10-3 mbar.

[0033] Though, the FIG. 1A shows a limited overview of the apparatus 100a but, it is to be understood that other embodiments are not limited thereto. The labels or names of the components are used only for illustrative purpose and does not limit the scope of the invention. Further, the apparatus 100a can include any number of components other than the components shown in the FIG. 1A.

[0034] FIG. IB shows the apparatus in which the Si and GaAs are placed separately to form Si doped GaN film by co-sputtering of the Si and the GaAs, according to the embodiments as disclosed herein. As depicted in the FIG. IB, the GaAs 104a and the Si 104b are placed separately in the vacuum chamber 102b. In an embodiment, power applied to the GaAs 104a and the Si 104b is varied for forming the Si doped GaN film on the substrate 106a.

[0035] The sputtering gas which includes argon-nitrogen is passed on to the Si 104b and the GaAs 104a through the gas inlet 108a. In an embodiment, the percentage of nitrogen in the sputtering gas is varied from 10 to 100% and the temperature in the chamber 102a is varied from room temperature to approximately 700 °C.

[0036] When the argon-nitrogen gas is passed on to the Si 104b and the GaAs 104a, argon-nitrogen gas sputters the Si 104b and the GaAs 104a. When the ionized nitrogen gas reacts with the sputtered GaAs 104a, the Si doped GaN film is formed on the substrate 106a. It should be noted that the Si doped GaN films are deposited as Si doped GaN layer on the substrate 106a when the argon-nitrogen gas interacts with the Si 104b and the GaAs 104a.

[0037] FIG. 1C shows an apparatus 100c in which the Si doped GaN film is formed by co-sputtering of the Si and the Gallium Arsenide (GaAs), where a gas inlet 108c is present external to the apparatus 100c, according to the embodiments as disclosed herein.

[0038] As depicted in the FIG. 1C, the apparatus 100c includes a vacuum chamber 102c, the GaAs 104a, the Si 104b, a substrate 106c and the gas inlet 108c.

[0039] In an embodiment, the gas inlet 108c can be present external to the apparatus 100c. The sputtering gas (argon-nitrogen gas mixture) is passed on the Si 104b and the GaAs 104a through the gas inlet 108c which is present external to the apparatus 100c as shown in the FIG. 1C.

[0040] It should be noted that the embodiments described in the

FIG. 1A for forming the Si doped GaN films, remain same for the FIG. 1C, though the gas inlet 108c is present external to the apparatus 100c. Although, the FIG. 1C shows that the Si 104b is placed on the GaAs 104a, the Si 104b can be placed separately in the vacuum chamber 102c as shown in the FIG. IB.

[0041] FIG. 2 is a flow chart illustrating a method for forming the silicon doped GaN films, according to the embodiments as disclosed herein. At step 202, the method 200 includes placing the Si 104b and the GaAs 104a in the vacuum chamber 102a. In an embodiment, the Si 104b is placed on the GaAs 104a. In another embodiment, the Si 104b and the GaAs 104a are placed separately in the vacuum chamber 102a.

[0042] In an embodiment, the Si 104b is placed on the GaAs 104a to co-sputter the Si 104b and the GaAs 104a. In an embodiment, the co- sputtering ratio of Si 104b and the target 104b can be varied by varying the percentage of area coverage of the GaAs erosion track with Si. It should be noted that the variation of the Si area coverage from 2 - 20 % is found to result in a change of carrier concentration of the GaN films from approximately 5 x 10 16 cm^" 3 to 2x1020 cm^" 3. [0043] At step 204, the method 200 includes passing argon-nitrogen gases into the vacuum chamber 102a and ionized to interact with the Si 104b and the GaAs 104a. In an embodiment, the sputtering gas which includes argon-nitrogen is passed on the Si GaAs 104a through the gas inlet 108a. In an embodiment, the percentage of nitrogen in the sputtering gas is varied from 10 to 100% and the temperature in the chamber 102a is varied from room temperature to approximately 700 °C.

[0044] At step 206, the method 200 includes forming the Si doped GaN in response to the interaction between argon-nitrogen gas mixture with the Si and the GaAs. When the argon-nitrogen gas is passed on the Si and GaAs, ionized argon-nitrogen gas sputters the Si and the GaAs. When the ionized nitrogen gas reacts with the GaAs, Si doped GaN film is formed on the substrate 106a. It should be noted that the Si doped GaN films are deposited on the substrate 106a when the argon-nitrogen gas interacts with the Si and the GaAs. Further, the GaN films are annealed at a temperature of 700 °C in nitrogen at a pressure on 8 x 10-3 mbar.

[0045] The various actions, acts, blocks, steps, or the like in the method 200 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.

[0046] Electrical resistivity and Hall measurements of Si doped GaN films were carried out in van der Pauw's geometry at room temperature. The GaN films were found to be n-type and the variation of their resistivity, carrier concentration and mobility with different deposition conditions was studied. A summary of these observations on Si doped GaN films are presented below.

[0047] The co-sputtering ratio of the Si 104b and the GaAs 104a was varied by pasting a small piece of Si 104b wafer on the GaAs 104a and varying the percentage of area coverage of the GaAs erosion track with Si. The variation of the Si area coverage from 2 - 20 % is found to result in a change of the carrier concentration of the films from approximately 5 xlO¹⁶ cm -^"3 to 2 xlO 20 cm -^"3. The highest values of carrier concentration and mobility are observed for Si coverage of 5-12 %. Typically for the Si coverage of 5 %, the variation of nitrogen percentage in the nitrogen-argon gas mixture is found to critically affect the electrical properties, as the carrier concentration is found to increase with decrease of nitrogen content in the sputtering atmosphere. Typically, a carrier concentration of approximately 10 17 cm -^"3 is observed for sputtering with 100 % nitrogen, and the carrier concentration increases to approximately 2x10 20 cm -^"3 for sputtering with 10 % nitrogen, while the films consist of single wurtzite phase GaN, with negligible arsenic (As) impurity. Below 10% nitrogen in the sputtering atmosphere, the films contain significant As and displays a poor crystalline quality due to the presence of GaAsN phase. The typical substrate temperature variation of the GaN films deposited with area coverage of 12 % and 20% nitrogen in the sputtering atmosphere, has shown a change of carrier concentration from approximately 10 18 cm -^"3 to approximately 2x10 1 cm -^"3 , when the substrate temperature is varied from 500 °C to 700 °C.

[0048] Thus, the proposed method has shown that the co-sputtering of Si and GaAs in argon-nitrogen gas can be used to vary the carrier concentration of Si-doped GaN films in a wide range from 5 xlO¹⁶ cm^"3 to 2 xlO 20 cm -^"3. It should be noted that the value of carrier concentration of 2 xlO²⁰ cm^"3 shows the highly degenerate, n⁺ doping of GaN films. The value of carrier concentration in Si-doped GaN films has usually been reported at relatively higher temperatures by MBE technique and not at all reported earlier by any other technique. Such n type and n⁺ type Si doped GaN films are very useful for application in a variety of GaN based devices, such as UV detectors, heterojunction field effect transistors, high electron mobility transistors, light emitting diodes and lasers. The low resistivity

(approximately 10 -^"3 ohm cm) and moderate mobility (10-20 cm 2 V-^"1 cm-^"1 ) of co-sputtered Si doped GaN films can be used as a transparent conducting electrode in a wide range of optoelectronic and transparent electronic devices based on nitrides.

[0049] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

STATEMENT OF CLAIMS We claim:

1. A method for forming silicon (Si) doped GaN films by a co-sputtering of Si and Gallium Arsenide (GaAs), with an argon-nitrogen gas mixture, the method comprising: forming Si doped GaN films in response to an interaction between said argon-nitrogen gas mixture with said Si and said GaAs.

2. The method of claim 1, wherein said Si is placed on said GaAs.

3. The method of claim 1, wherein said Si and GaAs are placed separately.

4. The method of claim 1, wherein a co-sputtering ratio of Si to said GaAs is varied to form said Si doped GaN films of different doping levels.

5. An apparatus comprising: a vacuum chamber with a gas inlet, wherein said chamber includes: a substrate; a target; wherein said substrate and said target are placed at a distance; wherein a Silicon (Si) and GaAs are placed in said vacuum chamber; wherein argon-nitrogen gases is passed through said inlet and ionized to interact with said Si and said GaAs; and wherein a Si doped GaN film is formed in response to said reaction. The apparatus of claim 5, wherein said Si is placed on said GaAs.

The apparatus of claim 5, wherein said Si and GaAs are placed separately.

The apparatus of claim 5, wherein a co-sputtering ratio of Si to said GaAs is varied to form said Si doped GaN films of different doping levels.