1. I have seen this happen !

2. You have exceeded your storage allocation

3. Creating a n-p junction on a p-type silicon wafer A n-p junction is a diode and a solar cell It can also be the start of a n-p-n bipolar transistor or a FET transistor Starting with a n-type wafer would create a p-n junction

4. Start with a clean p-type silicon wafer Clean silicon wafer P-type

5. A SiO 2 layer is deposited via PECVD on the backside to prevent backside doping Clean silicon wafer P-type Backside SiO2

6. Using a liquid n-type phosphorus spin on dopant, a layer of phosphorus is left on the surface Clean silicon wafer P - type Backside SiO2 Spin on phosphorus (n) dopant

7. To avoid contamination, a separate spinner is used for the spin on dopants This spinner is located in the yellow room closest to the garment change out room Spin at 3 KRPM for 20 seconds. Spin is preset for correct conditions Wafer held with vacuum. Vacuum switch is located on control panel

8. Liquid dopants are located in the dry box. Use P509 and always check the expiration date Use P509 – expiration date 1-30-2012

9. After diffusion @ 950 0 C a n-region is created in the silicon. Time and temperature determine the depth of the n doped region P doped silicon Backside SiO2 n doped silicon --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

10. High temperature tube furnace for 950 0 C diffusion Furnace #6 is for phosphorus doping only. Do not cross contaminate apparatus and tweezers. Verify correct temperature before using

11. An HF etch removes any residual phosphorus on the surface and the backside SiO 2 P-doped n doped -------------------------------------------------------------------------------------------------------------------------------------------------

12. A n/p junction has been formed P-doped n doped -------------------------------------------------------------------------------------------------------------------------------------------------

13. Solid phosphorus sources are available

14. Liquid POCl 3 with a nitrogen carrier gas is also used as a phosphorus dopant. POCl 3 will form HCl on exposure to moist air or water To high temperature furnace tube Nitrogen carrier gas in Constant temperature (20 0 C) cooler

15. A photo-mask will need to be created using AutoCAD Due to the current limitations on the tester in the clean room, cell size is limited to a maximum of 10 cm 2

16. Current solar light simulator in Cameron clean room with Keithley 4200 I/V tester @ 1 amp max

17. Example of a photo-mask transparency

19. AutoCAD dimension drawing must be submitted for approval Dimension Drawing is due in 2 weeks Any pattern for top side conductor is acceptable. Multiple top side conductor patterns preferred Cell size can vary from 2 cm 2 to 10cm 2 Patterns must be in-line to cut with the dicing saw

20. A new solar cell tester will be available in EPIC with higher current capability (10 amp)

21. The new tester will provide the capability to test standard size industrial cells 125mm x 125mm cell