As blue and other color LEDs are becoming more and more important, it is crucial to develop efficient p-type contacts.  P-type contacts are the metal connections to the p-type semiconductor in the device.  They need to be transparent so that the light produced by the LED can pass through them and be ohmic (conductive) so that the electrons can power the device.  The contacts that we will be researching are nickel-gold.     

This project builds on previous research and will correlate optical findings to their electrical properties.  The sheet resistance of the thin film will be measured using TLM (transmission line method).  Transmission line method involves deposition of test patterns onto thin films using photolithography and measuring the resistivity between them.  Another interesting study would be to find the upper limit of annealing effect on a light emitting diode.

Semester Two Midterm Update 3/2/2005

• Practiced and hopefully perfected the photolithography process

• Received training on the "Sputtering" machine so we could complete multiple tests ourselves

• Completed successful deposit of 2 kÅ gold on our test sample

• Completed successful liftoff using acetone and ultrasound.

• Attempted first photolithography procedure on the real samples from NIST
• This sample was damaged by the acetone during the cleaning process
• Completed photolithography process on second sample from NIST
• Attempt to deposit 2kÅ Au on this sample failed due to a device malfunction.  The sputtering machine failed to deposit the required amount of gold. This sample was not ruined however.

Upcoming Activities:

• Research why the sputtering machine failed
• Work to deposit 2kÅ Au on all of the test samples from NIST
• Use the probe station to measure resistivity
• Begin to correlate this resistance data with previous optical data
• Write final report

Progress Update 12/3/2004

• Completed deposition of 1u Au on test sample
• Attempt to lift off gold film using acetone and ultrasound was unsuccessful
• Researched possible reasons for failed lift off; determined Au should be deposited in a thinner coat and the lift off should be attempted within 48 hours of deposition

Upcoming Activities:

• Enhance photolithography procedure to obtain better results and make more samples
• Deposit 2kÅ Au on new test samples and perform lift off procedure of gold film
• Finish a formal project proposal report including progress made to date

Progress Report 11/4/2004

• Mask for test structures selected with appropriate CTLM structures
• Established a photolithography process
• Selection and preparation of amorphous SiO2 substrate with Ni/Au film
• Photolithography complete for first test sample  with encouraging results.
• Received CTLM analysis spreadsheet from Mike Ahrens
• Requested 1u Au deposition from John Hudak

Upcoming Activities:

• Inspect resulting CTLMs with optical microscopy
• Measure the sheet resistance with probe station

Progress Report 10/8/2004

• Preliminary research and paper search
• Gained access to the clean room
• Familiarization with clean room equipment
• Received photolithography test material (glass with metal thin film deposited) from Mike Ahrens
• Robert, Stewart and Matthew reviewed NIST research and LED basics.  The group also reviewed Robert's power point presentation on optical characterization of thin films.

Upcoming Activities:

• Deposit CTLM patterns in "thick" gold (1 micron thick)