Photodetector biasing scheme

1. Method, comprising:

providing a photodetector having a semiconductor conversion layer disposed between a first contact and a second contact, the second contact disposed over a surface of the semiconductor conversion layer opposite that of the first contact;

selecting to receive x-rays incident through the first or second contact of the photodetector; and

setting the bias for the first contact to be positive or negative with respect to the second contact to collect a lowest mobility carrier in the semiconductor conversion layer at the first contact if the first contact is selected to receive x-rays incident, and to collect a lowest mobility carrier in the semiconductor conversion layer at the second contact if the second contact is selected to receive x-rays incident.

2. The method of claim 1 , wherein setting the bias for the first contact relative to the second contact causes the highest mobility carrier in the semiconductor conversion layer to be collected at a location away from a contact selected to receive x-rays incident.

3. The method of claim 1 , wherein the semiconductor conversion layer comprises HgI 2 , and setting the bias comprises:

setting the bias for the first contact to be at a lower potential than the second contact to receive x-rays incident through the first contact; and

setting the bias for the first contact to be at a higher potential than the second contact to receive x-rays incident through the second contact.

4. The method of claim 1 , wherein the semiconductor conversion layer comprises PbI 2 , and setting the bias comprises:

setting the bias for the first contact to a higher potential than the second contact to receive x-rays incident through the first contact; and

setting the bias for the first contact to a lower potential than the second contact to receive x-rays incident through the second contact.

5. The method of claim 4 , wherein biasing comprises quasi-grounding the second contact and applying one of a negative voltage and a positive voltage to the first contact.

6. The method of claim 1 , wherein the semiconductor conversion layer comprises a plurality of semiconductor material layers.

7. The method of claim 1 , wherein the photodetector further comprises a substrate having a readout circuit coupled to the second contact and wherein the x-rays are received incident on the substrate, the x-rays being incident through the second contact with respect to the first contact.

8. The method of claim 3 , wherein the semiconductor conversion layer comprises a plurality of semiconductor material layers.

9. A method, comprising:

selecting a particular semiconductor material for a conversion layer of a photodetector;

determining a bias for the conversion layer; and

determining a surface of the conversion layer to receive incident x-rays based on a lowest mobility carrier of the particular semiconductor material selected and the determined bias.

10. The method of claim 9 , wherein the semiconductor material comprises PbI 2 and the bias is determined to be negative.

11. A photodetector, comprising:

a semiconductor conversion layer having a first surface and a second surface disposed opposite the first surface;

a first contact coupled to the first surface of the semiconductor conversion layer;

a second contact coupled to the second surface of the semiconductor conversion layer;

a substrate having a readout circuit coupled to the second contact, wherein the semiconductor conversion layer is configured to receive x-rays incident on the substrate of the photodetector; and

a bias circuit to set the bias for the second contact to be positive or negative with respect to the first contact, to collect at the second contact a lowest mobility carrier in the semiconductor conversion layer.

12. The photodetector of claim 11 , wherein the first contact is biased to a lower potential than the second contact.

13. The photodetector of claim 12 , wherein the first contact is negatively biased with respect to the second contact.

14. The photodetector of claim 13 , wherein the first contact is quasi-grounded and the second contact is coupled to a negative voltage.

15. The photodetector of claim 11 , wherein the readout circuit comprising an amplifier having a first input coupled to the negative voltage and a second input coupled to the second contact.

16. The photodetector of claim 11 , wherein the semiconductor conversion layer comprises PbI 2 .

17. The photodetector of claim 11 , wherein the semiconductor conversion layer comprises a plurality of semiconductor material layers.

18. The photodetector lf claim 4 , wherein the second contact comprises palladium.

19. The photodetector of claim 16 wherein the second contact comprises palladium.

20. The photodetector of claim 13 , wherein the second contact comprises palladium.

21. A photodetector, comprising:

means for directly converting x-rays to current, the means for directly converting disposed between a first and a second contact;

means for receiving x-rays incident on a substrate of the photodetector; and

means for setting the bias for biasing the second contact to be positive or negative with respect to the first contact, based on direction of x-ray incidence, to collect at the second contact a lowest mobility carrier in the semiconductor material.

22. The photodetector of claim 21 , wherein the second contact comprises means for providing a barrier to electron collection.

23. The photodetector of claim 22 , further comprising means for providing a signal from the second contact proportional to the received x-rays.