W/Si Schottky Diodes: Effect of Metal Deposition Conditions on the Barrier Height
- PDF / 358,447 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 37 Downloads / 180 Views
Permanentaddress : ElectronicEngineeringDepartment,Technion, 32000 Haifa,Israel. 149
Mat. Res. Soc. Symp. Proc. Vol. 356 ©1995 Materials Research Society
EXPERIMENTAL DETAILS. The samples used in this work were prepared by depositing (1000-5000)-A W films on p-type and n-type silicon wafers. Before their introduction in the dc-magnetron sputtering system, the silicon substrates were chemically cleaned using a standard procedure which included a last dip in HF. Prior to the deposition, the target (99.95% pure) was cleaned by presputtering for 5 min under the deposition conditions to be applied. The films were deposited at 100W- power at pressures varying between 5 10-3 and 10-1 mbar. The film stress was evaluated from the change in the substrate curvature after deposition by using a prof'lometer. The resistivity was measured with a four point probe. The microstructure of the W-films (phase identification, lattice parameter and grain size) was estimated from X-ray measurements. Schottky barrier contacts of different areas (0.071-0.384 mm 2 ) were defined by photolithography and selective etch. Schottky barrier height was determined using I-V measurements at room temperature. As a result of the low barrier height on p-type, the forward characteristic Ln(I) versus V is highly nonlinear and can not be used to infer IBp. 8 Therefore, OPBp was determined by the measurement of the reverse saturation current. The barrier height on n-type was determined by using the same procedure. But in this case, forward I-V characteristics were also used, the ideality factor is always close to 1. Therefore thermionic emission was supposed to govern current transport.
-y 50
do N] G]
40 •
30
[
= 0.080798+ 42.85xR=0.99975
18
areas
A=0.34MMm2
-
W/n.Si(1U1)
15
A=0.196amm2 A=0.126rmm2
=L
Arprmsure=8.10-intmr - Power11XOW
12
A=0-071MM2
9 20
6
Z 10 0 0.530
0 0.534
0.538 0.542 Barrier height (eV)
0
0.546
Figure-1 Distributionof Schottky barrier heights prepared on p-type silicon with diode areas varying from 0.071 mm 2 to 0.384 mm 2 .
0.1
0.2 Area (mm )
0.3
0.4
Figure-2 Variation of the main value of the reverse currentas afunction of the diode areas.
The current I, for n-type for example, is given by 9 (1) I = IS [ exp(qV/kT) - 11 Is was determined either by extrapolating the forward I-V characteristic to zero applied voltage or directly from a measurement of the current at a reverse voltage VR. IS is described by 9 IS = A* S T 2 exp [- OB / kT]
(2)
150
where A* (32 and 112 A/cm 2/K2 for p-type and n-type respectively) is the effective Richardson constant. (B is an effective barrier height which slightly depends on the voltage. It differs from the zero-field barriercT determined under flat-band conditions by C-V measurements and from the zero-voltage barrier height4 , deduced from forward characteristics. 0 is underestimated in our procedure and can be evaluated by taking into account the image force barrier lowering. The values of the barriers determined from the reverse and the forward current are always c
Data Loading...
