High electron mobility transistor (HEMT) comprising stacked nanowire or nanosheet heterostructures
View Patent ↗A high electron mobility transistor (HEMT) for high frequency applications comprises: a source and a drain spaced apart on a substrate, each of the source and drain extending vertically away from the substrate; a stack of nanowire or nanosheet heterostructures suspended between the source and the drain and being vertically separated from each other, each of the nanowire or nanosheet heterostructures comprising a channel layer between top and bottom barrier layers; a gate dielectric layer on each nanowire or nanosheet heterostructure; and a gate electrode on each gate dielectric layer. Each of the channel layers comprises a first group III nitride including aluminum, and each of the top and bottom barrier layers comprises a second group III nitride including a higher amount of aluminum than the first group III nitride. The stack includes N of the nanowire or nanosheet heterostructures, where N is an integer from 2 to 50.
1 . A high electron mobility transistor (HEMT) for high frequency applications, the HEMT comprising:
a source and a drain spaced apart on a substrate, each of the source and drain extending vertically away from the substrate;
a stack of nanowire or nanosheet heterostructures suspended between the source and the drain, the nanowire or nanosheet heterostructures being vertically separated from each other in an air-bridge formation, each of the nanowire or nanosheet heterostructures comprising a channel layer between top and bottom barrier layers;
a gate dielectric layer on each nanowire or nanosheet heterostructure; and
a gate electrode on each gate dielectric layer,
wherein each of the channel layers comprises a first group III nitride including aluminum, and wherein each of the top and bottom barrier layers comprises a second group III nitride including a higher amount of aluminum than the first group III nitride, and
wherein the stack includes N of the nanowire or nanosheet heterostructures, N being an integer from 2 to 50.
2 . The HEMT of claim 1 , wherein the first group III nitride and the second group III nitride comprise aluminum nitride, aluminum scandium nitride, aluminum indium scandium nitride, aluminum boron nitride, aluminum boron gallium nitride, aluminum boron scandium nitride, aluminum gallium nitride, and/or aluminum scandium gallium nitride.
3 . The HEMT of claim 1 , wherein the first group III nitride comprises Al x Ga 1-x N, wherein x≥0.3.
4 . The HEMT of 3 , wherein the channel layers of the nanowire or nanosheet heterostructures collectively comprise:
at least two and up to N different values of x, and/or
at least two and up to N different thicknesses.
5 . The HEMT of claim 1 , wherein the second group III nitride comprises Al y R z Ga 1-y-z N, wherein 0.6≤y≤1.0, 0≤z≤0.4, and R is selected from the group consisting of: B and Sc.
6 . The HEMT of claim 5 , wherein the top and bottom barrier layers of the nanowire or nanosheet heterostructures collectively comprise:
at least two and up to N different values of y, and/or
at least two and up to N different values of z, and/or
at least two and up to N different thicknesses.
7 . The HEMT of claim 1 , where the nanowire or nanosheet heterostructures are undoped.
8 . The HEMT of claim 1 , wherein the stack of nanowire or nanosheet heterostructures is a stack of nanowire heterostructures, and
wherein the gate electrode surrounds each of the nanowire heterostructures, the gate electrode having a gate-all-around configuration.
9 . The HEMT of claim 8 , wherein the stack of nanowire heterostructures is a first stack, and further comprising a second stack of nanowire heterostructures laterally spaced apart from the first stack and suspended between the source and the drain, the nanowire heterostructures of the second stack being vertically separated from each other.
10 . The HEMT of claim 1 , wherein the stack of nanowire or nanosheet heterostructures is a stack of nanosheet heterostructures, and
wherein the gate electrode comprises a top gate overlying each nanosheet heterostructure and a bottom gate underlying each nanosheet heterostructure, the top and bottom gates having a dual-gate configuration.
11 . The HEMT of claim 1 , wherein the dielectric layer has a thickness in a range from about 2 nm to about 10 nm, and
wherein the dielectric layer comprises Al 2 O 3 and/or HfZrO 2 .
12 . The HEMT of claim 1 , wherein a length of the gate electrode is in a range from about 30 nm to about 70 nm, and
wherein the substrate comprises GaN.
13 . The HEMT of claim 1 , wherein the source and the drain comprise In x Ga 1-x N, wherein 0≤x≤0.5, the source and the drain having a graded composition where x increases in a direction away from the substrate.
14 . The HEMT of claim 13 , wherein the In x Ga 1-x N comprises Si, Te, and/or Se as a dopant, and
wherein the In x Ga 1-x N is heavily doped, the In x Ga 1-x N comprising a dopant at a concentration of at least about 1×10 18 /cm 3 .
15 . The HEMT of claim 1 , wherein each nanowire or nanosheet heterostructure comprises a 2D electron gas.
16 . The HEMT of claim 1 comprising a cut-off frequency of at least about 25 GHz.
17 . The HEMT of claim 1 having a maximum output power of at least about 300 mW/mm per nanowire or nanosheet heterostructure.
18 . A power amplifier for use at frequencies above 90 GHz, the power amplifier comprising the HEMT of claim 1 .
19 . A method of making a high electron mobility transistor (HEMT), the method comprising:
epitaxially growing a stack of layers on a substrate, the stack of layers including N sacrificial layers comprising a sacrificial material alternating with N heterostructure layers, each of the heterostructure layers comprising a first group III nitride and a second group III nitride, where N is an integer and 2≤N≤50;
forming a source and a drain on the substrate alongside the stack of layers on a first side and a second side thereof, respectively, the stack of layers connecting the source and the drain;
removing the sacrificial layers comprising the sacrificial material so as to isolate the heterostructure layers, thereby forming a stack of nanosheet heterostructures suspended between the source and the drain and being vertically separated from each other in an air-bridge formation;
forming a gate dielectric layer on each of the nanosheet heterostructures; and
forming a gate electrode on the gate dielectric layer.
20 . A method of making a high electron mobility transistor (HEMT), the method comprising:
epitaxially growing a stack of layers on a substrate, the stack of layers including N sacrificial layers comprising a sacrificial material alternating with N heterostructure layers, each of the heterostructure layers comprising a first group III nitride and a second group III nitride, where N is an integer and 2≤N≤50;
forming a source and a drain on the substrate alongside the stack of layers on a first side and a second side thereof, respectively, the stack of layers connecting the source and the drain;
removing material from a third side and a fourth side of the stack of layers to define a stack of wires of a predetermined width connecting the source and the drain, the stack of wires comprising sacrificial nanowires of the sacrificial material alternating with heterostructure nanowires comprising the first group III nitride and the second group III nitride; and
removing the sacrificial nanowires comprising the sacrificial material so as to isolate the heterostructure nanowires, thereby forming a stack of nanowire heterostructures suspended between the source and the drain and being vertically separated from each other in an air-bridge formation;
forming a gate dielectric layer on each of the nanowire heterostructures; and
forming a gate electrode on the gate dielectric layer.
21 . The HEMT of claim 1 , comprising a positive threshold voltage.