Electronic device including a multiple channel HEMT
An electronic device can include a HEMT including at least two channel layers. In an embodiment, a lower semiconductor layer overlies a lower channel layer, wherein the lower semiconductor layer has an aluminum content that is at least 10% of a total metal content of the lower semiconductor layer. An upper semiconductor layer overlies the upper channel layer, wherein the upper semiconductor layer has an aluminum content that is greater as compared to the lower semiconductor layer. In another embodiment, an electronic device can include stepped source and drain electrodes, so that lower contact resistance can be achieved. In a further embodiment, an absolute value of a difference between pinch-off or threshold voltages between different channel layers is greater than 1 V and allows current to be turned on or turned off for a channel layer without affecting another channel layer.
1. An electronic device comprising:
a first channel layer;
a first semiconductor layer overlying the first channel layer, wherein the first semiconductor layer has a first aluminum content that is at least 10% of a total metal content of the first semiconductor layer;
a second channel layer overlying the first semiconductor layer; and
a second semiconductor layer overlying the second channel layer, wherein the second semiconductor layer has a second aluminum content that is greater than the first aluminum content.
2. The electronic device of claim 1 , wherein:
the first channel layer has a first pinch-off voltage;
the second channel layer has a second pinch-off voltage; and
an absolute value of a difference between the first and second pinch-off voltages is greater than 1 V.
3. The electronic device of claim 1 , wherein:
the first channel layer includes Al a Ga (1-a) N, wherein 0≦a≦0.1;
the first semiconductor layer includes Al b Ga (1-b) N, wherein 0.10≦b≦0.30;
the second channel layer includes Al c Ga (1-c) N, wherein 0≦c≦0.15; and
the second semiconductor layer includes Al d Ga (1-d) N, wherein 0.15≦d≦0.35.
4. The electronic device of claim 3 , wherein a=0, and c=0.
5. The electronic device of claim 1 , further comprising a substrate and a buffer layer overlying the substrate, wherein the buffer layer is disposed between the substrate and the first channel layer.
6. The electronic device of claim 5 , wherein the first channel layer is thicker than the second channel layer and has a thickness of at most 1000 nm.
7. The electronic device of claim 1 , wherein the electronic device comprises a high voltage transistor that includes the first and second channel layers.
8. The electronic device of claim 7 , further comprising:
a passivation layer overlying the second semiconductor layer; and
a gate electrode, wherein at least a portion of the passivation layer is disposed between the gate electrode and the second channel layer.
9. The electronic device of claim 8 , wherein the passivation layer comprises:
a first insulating nitride layer overlying the second semiconductor layer;
a III-N layer overlying the first insulating nitride layer; and
a second insulating nitride layer overlying the III-N layer.
10. The electronic device of claim 1 , wherein each of the first and second channel layers and the first and second semiconductor layers has a dopant concentration of at most 1×10 15 atoms/cm 3 .
11. The electronic device of claim 1 , further comprising:
a substrate;
a buffer layer overlying the substrate;
a passivation layer overlying the second semiconductor layer; and
a gate electrode configured to control the first and second channel layers,
wherein:
the electronic device comprises a double channel power HEMT;
the first channel layer is a first GaN channel layer overlying the buffer layer, wherein the first GaN channel layer has a thickness in a range of 11 nm to 1000 nm;
the first semiconductor layer includes Al b Ga (1-b) N, wherein 0.10≦b≦0.30 and has a thickness in a range of 10 nm to 40 nm;
the second channel layer is a second GaN channel layer overlying the first semiconductor layer is thinner than the first channel layer, and has a thickness in a range of 10 nm to 200 nm;
the second semiconductor layer has a greater aluminum content as compared to the first semiconductor layer, includes Al d Ga (1-d) N, wherein 0.15≦d≦0.35 and has a thickness in a range of 10 nm to 40 nm;
the first channel layer has a first pinch-off voltage;
the second channel layer has a second pinch-off voltage; and
an absolute value of a difference between the pinch-off voltages of the first and second channel layers is greater than 2 V.
12. An electronic device comprising:
a substrate;
a first channel layer overlying the substrate;
a second channel layer overlying the first channel layer;
a source electrode overlying the substrate; and
a drain electrode overlying the substrate,
wherein:
the source electrode, the drain electrode or each of the source and drain electrodes includes a first portion and a second portion;
the substrate is closer to the first portion as compared to the second portion;
for current flowing through the first channel layer, more current flows through the first portion than through the second portion; and
for current flowing through the second channel layer, more current flows through the second portion than through the first portion.
13. The electronic device of claim 12 , further comprising:
a first semiconductor layer disposed between the first and second channel layers; and
a second semiconductor layer overlying the second channel,
wherein the first portion extends through the second channel layer and the second semiconductor layer, and the second portion does not extend through the second channel layer or to the first channel and first semiconductor layers.