Enhancement mode GaN HEMT device and method for fabricating the same
An enhancement-mode GaN transistor and a method of forming it. The enhancement-mode GaN transistor includes a substrate, transition layers, a buffer layer comprised of a III Nitride material, a barrier layer comprised of a III Nitride material, drain and source contacts, a gate III-V compound containing acceptor type dopant elements, and a gate metal, where the gate III-V compound and the gate metal are formed with a single photo mask process to be self-aligned and the bottom of the gate metal and the top of the gate compound have the same dimension. The enhancement mode GaN transistor may also have a field plate made of Ohmic metal, where a drain Ohmic metal, a source Ohmic metal, and the field plate are formed by a single photo mask process.
1. A method of forming an enhancement mode GaN transistor, the method comprising:
nucleating and growing transition layers on a substrate;
growing an III Nitride EPI layer over the transistor layers;
growing an III Nitride barrier layer over the EPI layer;
growing a GaN layer with acceptor type dopants over the barrier layer;
depositing a gate contact layer on the doped GaN layer;
applying a gate photo resistant pattern;
etching away the gate contact layer outside the gate region;
etching away the doped GaN layer, except a portion of the doped GaN layer beneath the gate contact;
removing the gate photo resistant pattern;
depositing a dielectric layer;
applying a contact photo resistant pattern;
etching the dielectric layer to open the drain and source contact area;
removing the contact photo resistant pattern;
depositing an Ohmic contact metal;
applying a metal photo resistant pattern;
etching the Ohmic contact metal;
removing the metal photo resistant pattern; and
performing rapid thermal annealing to form Ohmic drain and source contacts.
2. The method of claim 1 , wherein the EPI layer is comprised of InAlGaN.
3. The method of claim 1 , wherein the barrier layer is comprised of InAlGaN with a larger band gap than the buffer layer.
4. A method of forming an enhancement mode GaN transistor, the method comprising:
nucleating and growing transition layers on a substrate;
growing an InAlGaN EPI layer over the transistor layers;
growing an InAlGaN barrier layer over the InAlGaN EPI layer;
growing an InAlGaN layer with acceptor type dopants over the InAlGaN barrier layer;
growing a GaN layer with acceptor type dopants over the doped InAlGaN layer;
depositing a gate contact layer on the doped GaN layer
applying a gate photo resistant pattern;
etching away the gate contact layer outside the gate region;
etching away the doped GaN layer and the doped InAlGaN layer, except for portions of the doped GaN layer and the doped InAlGaN layer beneath gate contact;
removing the gate photo resistant pattern;
depositing a dielectric layer;
applying a contact photo resistant pattern;
etching the dielectric layer to open the drain and source contact area;
removing the contact photo resistant pattern;
depositing an Ohmic contact metal;
applying a metal photo resistant pattern;
etching the Ohmic contact metal;
removing the metal photo resistant pattern; and
performing rapid thermal annealing to form Ohmic drain and source contacts.
5. A method of forming an enhancement mode GaN transistor, the method comprising:
nucleating and growing transition layers on a substrate;
growing an InAlGaN EPI layer over the transistor layers;
growing an AlGaN barrier layer over the InAlGaN EPI layer;
growing an AlGaN layer with acceptor type dopants over the AlGaN barrier layer;
growing a GaN layer with acceptor type dopants over the doped AlGaN layer;
depositing a gate contact layer on the doped GaN layer
applying a gate photo resistant pattern;
etching away the gate contact layer outside the gate region;
etching away the doped GaN layer, except for portions of the doped GaN layer and the doped AlGaN layer beneath gate contact;
removing the gate photo resistant pattern;
applying another photo resistant pattern;
etching the doped AlGaN layer such that the doped AlGaN extends outside the gate region towards the drain;
removing the photo resistant pattern;
depositing a dielectric layer;
applying a contact photo resistant pattern;
etching the dielectric layer to open the drain and source contact area;
removing the contact photo resistant pattern;
depositing an Ohmic contact metal;
applying a fourth photo resistant pattern;
etching the Ohmic contact metal
removing the fourth photo resistant pattern; and
performing rapid thermal annealing to form Ohmic drain and source contacts.