Transistor device and method

1. A heterojunction bipolar transistor device for operation as a field-effect transistor device which is responsive to an input voltage for application to a base/gate terminal to control current flow between an emitter/source terminal and a collector/drain terminal, comprising:

a layered semiconductor heterojunction structure including a base/gate layer of a first semiconductor type disposed between an emitter/source layer of a second semiconductor type and a collector/drain layer of said second semiconductor type;

said emitter/source layer comprising a higher bandgap material than said base/gate layer;

said base/gate layer having a thickness of less than about 100 Angstroms;

an emitter/source terminal coupled with said emitter/source layer, a base/gate terminal coupled with said base/gate layer, and a collector/drain terminal coupled with said collector/drain layer;

whereby, application of said input voltage to said base/gate terminal is operative to control current flow between said emitter/source and said collector/drain.

2. The device as defined by claim 1 , wherein said first semiconductor type is p-type, and said second semiconductor layer is n-type.

3. The device as defined by claim 1 , wherein said first semiconductor type is n-type, and said second semiconductor layer is p-type.

4. The device as defined by claim 1 , wherein said layered semiconductor heterojunction structure has the construction of a vertical stack of layers on a semiconductor substrate.

5. The device as defined by claim 1 , wherein said input voltage is an AC voltage having a frequency of at least 100 GHz, and wherein the input impedance to said base/gate terminal has a relatively very high resistive component as compared to its reactive component at the frequency of said AC voltage.

6. The device as defined by claim 5 , wherein said resistive component is at least an order or magnitude greater than said reactive component at the frequency of said AC voltage.

7. The device as defined by claim 1 , wherein said base/gate layer and said collector/drain layer also comprise respective materials having different bandgaps.

8. The device as defined by claim 4 , wherein said base/gate layer and said collector/drain layer also comprise respective materials having different bandgaps.

9. The device as defined by claim 1 , wherein said base/gate layer is highly doped.

10. The device as defined by claim 1 , wherein said base/gate layer is doped to a doping concentration of at least 10 19 /cm 3 .

11. The device as defined by claim 1 , further comprising at least one layer, within said base/gate layer, that exhibits quantum size effects.

12. The device as defined by claim 7 , further comprising at least one layer, within said base/gate layer, that exhibits quantum size effects.

13. The device as defined by claim 11 , wherein said at least one layer that exhibits quantum size effects comprises a quantum well layer.

14. The device as defined by claim 1 , wherein said base/gate layer is compositionally graded.

15. A field-effect transistor device, comprising:

a semiconductor heterostructure comprising, in a vertically stacked configuration, a semiconductor gate layer between semiconductor source and drain layers, said layers being separated by heterosteps;

said gate layer having a thickness of less than about 100 Angstroms; and

source, gate, and drain electrodes respectively coupled with said source, gate, and drain layers.

16. The device as defined by claim 15 , wherein said gate layer is p-type semiconductor, and said source and drain layers are n-type semiconductor.

17. The device as defined by claim 15 , wherein said source and drain layers are p-type semiconductor, and said gate layer are n-type semiconductor.

18. The device as defined by claim 15 , wherein said gate layer is highly doped.

19. The device as defined by claim 15 , wherein said gate layer is doped to a doping concentration of at least 10 19 /cm 3 .

20. The device as defined by claim 15 , wherein said input voltage is an AC voltage having a frequency of at least 150 GHz, and wherein the input impedance to said base/gate terminals has a relatively very high resistive component as compared to its reactive component at the frequency of said AC voltage.

21. The device as defined by claim 20 , wherein said resistive component is at least an order or magnitude greater than said reactive component at the frequency of said AC voltage.

22. The device as defined by claim 15 , further comprising at least one layer, within said gate layer, that exhibits quantum size effects.

23. A method for operating a transistor device as a field-effect transistor device which is responsive to an input voltage for application to a base/gate terminal to control current flow between an emitter/source terminal and a collector/drain terminal, comprising steps of:

providing a layered semiconductor heterojunction structure including a base/gate layer of a first semiconductor type disposed between an emitter/source layer of a second semiconductor type and a collector/drain layer of said second semiconductor type; said emitter/source layer comprising a higher bandgap material than said base/gate layer; and said base/gate layer having a thickness of less than about 100 Angstroms;

providing an emitter/source terminal coupled with said emitter/source layer, a base/gate terminal coupled with said base/gate layer, and a collector/drain terminal coupled with said collector/drain layer; and

applying said input voltage to said base/gate terminal to control current flow between said emitter/source and said collector/drain.

24. The method as defined by claim 23 , wherein said step of providing a layered semiconductor heterojunction structure comprises depositing a vertical stack of layers on a semiconductor substrate.

25. The method as defined by claim 23 , wherein said step of applying an input voltage to said base/gate terminal comprises applying an AC voltage, and further comprising providing said base/gate layer such that the input impedance to said base/gate terminal has a relatively very high resistive component as compared to its reactive component at the frequency of said AC voltage.

26. The method as defined by claim 25 , wherein said resistive component is at least an order or magnitude greater than said reactive component at the frequency of said AC voltage.

27. The method as defined by claim 25 , wherein said AC voltage has a frequency of at least 100 GHz.

28. The method as defined by claim 23 , wherein said step of depositing layers includes depositing said base/gate layer and said collector/drain layer with respective materials having different bandgaps.