ACCENT PN4400 ECV (Electrochemical

C-V

Profiler) is specially designed for the semiconductor materials with wide band gap.At present

it is mainly used for GaN.GaN is difficult to etch normally.But if it was lit by UV light

it can be etched by H

2

SO

4

.According to our experience

this make ECV to be specially suitable for GaN.Becase no lighting no etching

uniform light makes uniform etch.What should be point out is that this rule is only limited to GaN:Si.For our wafer with whole LED structure

it is very difficult to get uniform etch on p layer.To get uniform etch

it is still very important to select carefully the ecth and measure conditions.One tip is that you must stop the etch process temperarily to check and change the conditions

and from time to time

stop to elimit the bubbler near the etch hole edge by an injector filled with H

2

SO

4

. Because it will take a long time to wait the LED chip result after wafer growth.It will be better to find out a relationship between the chip result and the ECV result.Two samples with different buffer technology produced in the MOCVD system made by Thomas Swan Ltd.were measured by PN4400 ECV.From the relation of carrier concentration vs.depth

it is easy to see that the lowest carrier concentration given by ECV can be used as a standard to judge the crystal quality.Two samples were made into LED chips.It is known to us all that the

I

r

of LED has a close relationship with the crystal quality.The sample with the lower minimum carrier concentration gives lower

I

r

.Besides the carrier concentration distribution

ECV profiler can also give a lot of other information abou GaN.So as the experience accumulates

we believe that ECV profiler can give some important information about GaN wafer before it becomes LED chips.Silicon dopping technology is very important for fabrication of GaN LED.Certainly

the silicon will diffuse in GaN at high temperature.So it is important to find the silicon diffusion coefficient in GaN.We try to do this by ECV.By introducing a diffusion model and Gaussian fitting

we estimate that the silicion diffusion coefficient in GaN at 1 030℃ is below 4.3×10

-18

m

2

/s.