Composite-channel high electron mobility transistor
AssigneeWolfspeed, Inc.
InventorSriram Saptharishi
Life of this patent
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Abstract
A HEMT comprises a composite channel, made up of a plurality of channel/barrier layer heterojunctions. That is, two or more channel/barrier layer pairs are deposited on a substrate, under a gate contact. A separate 2DEG is formed in each channel layer at the heterojunction with the barrier layer. The HEMT channel is effectively divided among a plurality of parallel 2DEGs. A high total charge density—required for high power operation—is divided among the plurality of 2DEGs. Since each 2DEG does not have a large charge density, it can sustain the high saturated electron velocity required for very high frequency operation. The composite-channel HEMT thus operates with high gain, at high power levels, and at high frequencies.
Claims36
A composite channel transistor, comprising:
- a first channel layer;
- a first barrier layer on the first channel layer, the first barrier layer having a higher bandgap than the first channel layer;
- a first Two-Dimensional Electron Gas (2DEG) formed in the first channel layer at an interface with the first barrier layer;
- and
- a second channel layer on the first barrier layer;
- a second barrier layer on the second channel layer, the second barrier layer having a higher bandgap than the second channel layer;
- and
- a second 2DEG formed in the second channel layer at an interface with the second barrier layer;
- wherein a composite channel of the transistor comprises both the first and second 2DEGs;
- and
- wherein electron charge density is shared between the first and second 2DEG such that the overall saturated electron velocity in the composite channel is greater than in a channel of a transistor having only one 2DEG formed by a channel and barrier layer having properties substantially similar to the first or second channel and barrier layers.
A method of fabricating a transistor, comprising:
- depositing a first channel layer;
- depositing a first barrier layer on the first channel layer, the first barrier layer having a higher bandgap than the first channel layer, whereby a first Two-Dimensional Electron Gas (2DEG) is formed in the first channel layer at an interface with the first barrier layer;
- depositing a second channel layer on the first barrier layer;
- and
- depositing a second barrier layer on the second channel layer, the second barrier layer having a higher bandgap than the second channel layer, whereby a second 2DEG is formed in the second channel layer at an interface with the second barrier layer;
- wherein a composite channel of the transistor comprises both the first and second 2DEGs;
- and
- wherein electron charge density is shared between the first and second 2DEG so as to increase the overall saturated electron velocity in the composite channel;
- wherein electron charge density is shared between the first and second 2DEG such that the overall saturated electron velocity in the composite channel is greater than in a channel of a transistor having only one 2DEG formed by a channel and barrier layer having properties substantially similar to the first or second channel and barrier layers.
A composite channel transistor, comprising:
- a first channel layer comprising GaN;
- a first barrier layer on the first channel layer, the first barrier layer comprising AlGaN;
- a first Two-Dimensional Electron Gas (2DEG) formed in the first channel layer at an interface with the first barrier layer;
- and
- a second channel layer comprising GaN;
- a second barrier layer on the second channel layer, the second barrier layer comprising AlGaN;
- and
- a second 2DEG formed in the second channel layer at an interface with the second barrier layer;
- wherein the concentration of Al in an embedded barrier layer is graded from a lower concentration at the lower surface to a higher concentration at the upper surface;
- and
- wherein the concentration of Al in the uppermost barrier layer is not graded as a function of depth.
Dependencies are inferred from the claim text.