Low sheet resistance GaN channel on Si substrates using InAlN and AlGaN bi-layer capping stack
First Claim
1. A method to form transistor layers comprising:
- forming a GaN channel layer comprising (1) GaN material on a top surface of a substrate (2) a capping AlN layer that has a thickness of between 0.6 and 1.5 nanometers on the GaN material, wherein the GaN channel layer includes islands of GaN material formed between islands that consist of oxide material only that are completely buried under a thickness of the GaN material;
forming a bi-layer capping stack on a top surface of the GaN channel layer, wherein forming the bi-layer capping stack includes;
forming a lower capping AlGaN layer of AlGaN material on a top surface of a capping AlN layer comprising AlN material and excluding Indium formed on the top surface of the GaN channel layer; and
forming an upper capping AlInN layer of AlInN material on a top surface of the AlGaN material, wherein the AlGaN layer comprises AlXGa(1-X)N, where X is less than 0.4; and
wherein the AlInN layer is AlYIn(1-Y)N, where Y is greater than 0.8, wherein a top surface of the AlGaN material forms a setback material surface upon which the AlInN material may be selectively etched, wherein the AlGaN layer has a thickness of between 2 and 10 nm, and causes an electron density of greater than 2.5 E13 cm/2; and
wherein the AlInN layer has a thickness of between 5 and 15 nm, and causes a channel mobility of between 900 and 1000 CM2/V-s, wherein the bi-layer capping stack causes a sheet resistance of between 200 and 300 ohms per SQR in a 2DEG channel formed in a upper thickness of the GaN layer.
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Abstract
Transistors or transistor layers include an InAlN and AlGaN bi-layer capping stack on a 2DEG GaN channel, such as for GaN MOS structures on Si substrates. The GaN channel may be formed in a GaN buffer layer or stack, to compensate for the high crystal structure lattice size and coefficient of thermal expansion mismatch between GaN and Si. The bi-layer capping stack an upper InAlN layer on a lower AlGaN layer to induce charge polarization in the channel, compensate for poor composition uniformity (e.g., of Al), and compensate for rough surface morphology of the bottom surface of the InAlN material. It may lead to a sheet resistance between 250 and 350 ohms/sqr. It may also reduce bowing of the GaN on Si wafers during growth of the layer of InAlN material, and provide a AlGaN setback layer for etching the InAlN layer in the gate region.
24 Citations
26 Claims
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1. A method to form transistor layers comprising:
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forming a GaN channel layer comprising (1) GaN material on a top surface of a substrate (2) a capping AlN layer that has a thickness of between 0.6 and 1.5 nanometers on the GaN material, wherein the GaN channel layer includes islands of GaN material formed between islands that consist of oxide material only that are completely buried under a thickness of the GaN material; forming a bi-layer capping stack on a top surface of the GaN channel layer, wherein forming the bi-layer capping stack includes; forming a lower capping AlGaN layer of AlGaN material on a top surface of a capping AlN layer comprising AlN material and excluding Indium formed on the top surface of the GaN channel layer; and forming an upper capping AlInN layer of AlInN material on a top surface of the AlGaN material, wherein the AlGaN layer comprises AlXGa(1-X)N, where X is less than 0.4; and
wherein the AlInN layer is AlYIn(1-Y)N, where Y is greater than 0.8, wherein a top surface of the AlGaN material forms a setback material surface upon which the AlInN material may be selectively etched, wherein the AlGaN layer has a thickness of between 2 and 10 nm, and causes an electron density of greater than 2.5 E13 cm/2; and
wherein the AlInN layer has a thickness of between 5 and 15 nm, and causes a channel mobility of between 900 and 1000 CM2/V-s, wherein the bi-layer capping stack causes a sheet resistance of between 200 and 300 ohms per SQR in a 2DEG channel formed in a upper thickness of the GaN layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Transistor layers comprising:
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a GaN channel layer comprising (1) GaN material on a top surface of a substrate, (2) a capping AlN layer that has a thickness of between 0.6 and 1.5 nanometers on the GaN material, wherein the GaN channel layer includes islands of GaN material formed between islands that consist of oxide material only that are completely buried under a thickness of the GaN material; a bi-layer capping stack on a top surface of the GaN channel layer, wherein the bi-layer capping stack includes; a lower capping AlGaN layer of AlGaN material on a top surface of a capping AlN layer comprising AlN material and excluding Indium on the top surface of the GaN channel layer; and an upper capping AlInN layer of AlInN material on a top surface of the AlGaN material, wherein the AlGaN layer comprises AlXGa(1-X)N, where X is less than 0.4; and
wherein the AlInN layer is AlYIn(1-Y)N, where Y is greater than 0.8, wherein a top surface of the AlGaN material forms a setback material surface upon which the AlInN material may be selectively etched, wherein the AlGaN layer has a thickness of between 2 and 10 nm, and causes an electron density of greater than 2.5 E13 cm/2; and
wherein the AlInN layer has a thickness of between 5 and 30 nm, and causes a channel mobility of between 900 and 1400 CM2/V-s, wherein the bi-layer capping stack causes a sheet resistance of between 200 and 300 ohms per SQR in a 2DEG channel formed in a upper thickness of the GaN layer. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. A system for computing comprising:
a microprocessor coupled to a memory, the microprocessor having at least one electronic transistor having transistor layers comprising; a GaN channel layer comprising (1) GaN material on a top surface of a substrate (2) a capping AlN layer that has a thickness of between 0.6 and 1.5 nanometers on the GaN material, wherein the GaN channel layer includes islands of GaN material formed between islands that consist of oxide material only that are completely buried under a thickness of the GaN material; a bi-layer capping stack on a top surface of the GaN channel layer, wherein the bi-layer capping stack includes; a lower capping AlGaN layer of AlGaN material on a top surface of a capping AlN layer comprising AlN material and excluding Indium on the top surface of the GaN channel layer; and an upper capping AlInN layer of AlInN material on a top surface of the AlGaN material, wherein the AlGaN layer comprises AlXGa(1-X)N, where X is less than 0.4; and
wherein the AlInN layer is AlYIn(1-Y)N, where Y is greater than 0.8, wherein a top surface of the AlGaN material forms a setback material surface upon which the AlInN material may be selectively etched, wherein the AlGaN layer has a thickness of between 2 and 10 nm, and causes an electron density of greater than 2.5 E13 cm/2; and
wherein the AlInN layer has a thickness of between 5 and 15 nm, and causes a channel mobility of between 900 and 1400 CM2/V-s, wherein the bi-layer capping stack causes a sheet resistance of between 200 and 300 ohms per SQR in a 2DEG channel formed in a upper thickness of the GaN layer.- View Dependent Claims (19, 20, 21, 22, 23)
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24. A method to form transistor layers comprising:
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forming a GaN channel layer comprising (1) GaN material on a top surface of a substrate and (2) a capping AlN layer that has a thickness of between 0.6 and 1.5 nanometers on the GaN material, wherein the GaN channel layer includes islands of GaN material formed between islands that consist of oxide material only that are completely buried under a thickness of the GaN material; forming a bi-layer capping stack on a top surface of the GaN channel layer, wherein forming the bi-layer capping stack includes; forming a lower capping AlGaN layer of AlGaN material on a top surface of a capping AlN layer comprising AlN material and excluding Indium formed on the top surface of the GaN channel layer; forming an upper capping AlInN layer of AlInN material on a top surface of the AlGaN material, wherein the AlGaN layer has a thickness of between 2 and 10 nm, and causes an electron density of greater than 2.5 E13 cm/2; and
wherein the AlInN layer has a thickness of between 5 and 15 nm, and causes a channel mobility of between 900 and 1000 CM2/V-s, wherein the bi-layer capping stack causes a sheet resistance of between 200 and 300 ohms per SQR in a 2DEG channel formed in a upper thickness of the GaN layer;selectively etching the AlInN material to expose a top surface of the AlGaN material, wherein selectively etching the AlInN material comprises using a wet etch including a solution to selectively etch the AlInN material but not etch the AlGaN material; forming a gate dielectric over all of the exposed surface of the AlGaN material; and forming a metal gate electrode on the gate dielectric. - View Dependent Claims (25, 26)
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Specification