Transient and quiescent electric conductivity in silicon after electron irradiation at room temperatur

Horiye, H.

Naber, J. A.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19670016343 2020-03-16T18:19:19+00:00Z
GENERAL DYNAMICS
General Atomic Division
SPECIAL NUCLEAR EFFECTS LABORATORY
P.O. 9OX eoa. SAN 01900. CALWORN1A 02118
GAcn-6249
(12/31/66)
Copy No.
RADIATION EFFECTS ON SILICON
Eighth Quarterly Progress Report Covering the Period
October 1, 1966, through December 31, 1966
Work done by:	 Report written by:
J. B. Bryant
	
J. A. Haber
H. Horiye	 H. Horiye
J. A. Naber
E. G. Wikner
This is an informal progress- report prepared by the General Atomic
Divisionof General Dynamics Corporation under the contract deitgnated
below for sabinittai to the contracting agency. The results and datamay
be preliminary or tentative and therefore are subject to 1 evision or cor-
rection. This report may contain patentable material on which, patent
applications have not yet been filed by General Dynamics Corporation
or by the contracting agency, and further distribution of this report
should not be made without the prior approval of the contracting agency
or General Atomic.
National Aeronautics and Space Administration
Contract NAS7-289
General Atomic Project 430	 January 10, 1967
.$^• :^-25g7^
i	 1ACC[tD1ON NUMS[R!
LJ	 1 O[*!
[AU Q-
 -*2. fP* i o.
1NAfA CR OR TMX OR AD
NLM^[R!
.
1TNRW
(COD
1CAT[OORT!
1. INTRODUUTION
This eighth quarterly progress report on Contract NAS7-269, "Radiation
Effects in Silicon Solar Cells," covers the period October 1, 1966)
through December 31, 1966-
During this period, transient and quiescent electrical conductivity in
high-purity n-type silicon were investigated by the microwave technique
after irradiation by 30 MeV electrons at room temperature. Dc electrical
conductivity transient measurements on silicon samples of carrier con-
centration about 1014 cm-3 are being performed.
2. MICROWAVE CONDUCTIVITY
Quiescent and transient electrical conductivity in high-purity n-type
silicon were investigated by the microwave technique. As reported in the
last quarterly report, GACD -6249 (9/3o/6C-), for the high-resistivity
n-type silicon samples irradiated at room temperature, the electron flux
was not controlled sufficiently so that the radiation-induced recombination
center was not detected. Only a trapping center wao detected. During
this quarter, a high-resistivity n-type silicon sample was irradiated at
room temperature and the flux was controlled so that the introduction of
the recombination center was detected.
2.1 LINAC IRRADIATION
The sample used was n-type silicon of 10 4 ohm-cm resistivity and
an initial lifetime of 10 3 µsec at room temperature. The sample was
vacuum float zone. The pre-irradiation lifetime measurements on this
sample were obtained uping the General Atomic flash x-ray machine. The
pre-irradiation quiescent electrical conductivity results are shown in
Fig. 1. Figure 2 shows the pre-irradiation lifetime as analyzed using
the Shockley-Read theory. (1) The lifetime of this high-purity n-type
silicon at room temperature for a 0.5 rad (Si) injection level was about
1, 300 µsec .
The samples and the microwave apparatus were then moved to the General
Atomic electron linear accelerator (Linac) where extra precautions were
taken so that dur;ng Linac tuning the sample was not irradiated with high-
energy electrons. At low Linac dose rate (about 0.5 rad (Si)), the life-
time before high-energy electron irradiation was still about 1,300 µsec.
1
co
U
Fi
U
tZ
q-IO
0
O
^i
U
W
10 Q
W-3
20-4
r4
r.
1A-S
r
s
io-6
1	 ^
b
ol^ 0U
^-I
U
Sri
U
U
O
+0
t
a^
t
ao
w
2	 4	 6	 8	 to	 u	 ^'
ioo/s (Orr)
10 
Q ^Th
a
103
	 0 
Q	 r
O
102
0
0	 0	 0
10	 0
0
0
1
2	 4	 6	 8	 10	 12	 14
1000/T (°1C 1)
Fig. 2--Pre-irradiation carrier lifetime as a
function of inverse temperature
3
Therefore, during tuning the lifetime was not degraded, The sample was
then irradiated with 30 MeV, 0.1 µsec, 5 rads (Si) pulses of electrons.
The lifetime degradation was plotted according to the relationship
1 a 1 +4T	 TO
where To is the initial lifetime before irradiation, cp is the integrated
flux, K is the damage constant, and T is the lifetime afte-- an integrated
flux cp. Figure 3 shows the degradation of the lifetime of the high-
resistivity n-type silicon sample where 1/T is plotted as function of
y. The slope of the curve is the damage constant (K) equal to
2.2 x 10-8 cm2/sec at room temperature. During this irradiation the
lifetime was degraded at room temperature by a factor of 4. At this
point the irradiation was halted and the sample and microwave equipment
were moved to the flash x-ray facility where the temperature dependence
of the lifetime was checked. Figure 4 shows the results of this experi-
ment. This plot shows presence of both a recombination and a trapping
center. Figure 5 shows the quiescent conductivity after the initial
high-energy electron irradiation.
The sample was then taken back to Linac and irradiated again with
30 MeV electrons. Thic time the lifetime at room temperature was degraded
to about 70 µsec. The temperature characteristics of the lifetime of
these additional centers were then investigated at the flash x-ray facility,
The data for the experiment described in this paragraph has not been
completely analyzed. The analysis will be completed in the near future.
2.2 CONWNTS
The pre-irradiation lifetime of the high-resistivity silicon sample
was analyzed using the Shockley-Read theory. Figure 1 shows the inverse
temperature dependence of T t and T  as defined in GACD-6249 (9/30/66).
Comparison of Figures 1 and 5 shows that during the Linac irradiation
there was no detectable change in electrical conductivity. However, a
;omparison of Figures 2 and 4 shows a definite change in the inverse
temperature characteristics of the lifetime. The post-irradiation figure
indicates two centers present in the irradiated sample, one a recombina-
tion center and the other a trapping center. The value of
4
(x 10-3)
.1
6
5
4
P4
i^
^, 3
	 0
2
1
400	 800	 1200	 1600	 2000	 2400
ip (rads Si)
Fig- 3- -Inverse Lifetime as a function of
integrated electron flux
5
j03
v
M
102
10
104
2	 4	 6	 9	 10	 12	 14
UM/T (°f1)
Fig. 4--Carrier lifetime as a function of inverse
temperature after Linac irradiation
6
O10"'
O
10-4 	O
10-5
10-6
10-7
O
2	 4	 6	 8	 10	 12	 14
1000/T (Of')
Fig- 5--Electrical conductivity after Linac irradia-
tion as a function of inverse temperature
7
2.2 x 10 8 cm2fsec for the damage constant is about the same as has been
reported previously for n-type silicon. (2)
It should be noted that the trapping center introduced after the
room-temperature Linac irradiation is similar to the trapping center
introduced in high-resistivity n-type silicon irradiated by high-energy
electrons at 4.20K.(3)
Further information about the recombination and trapping center no
doubt will be available after the remainder of the experiment is analyzed.
2.3 F'tJT W PUNS
Once the remainder of the Linac irradiation data on this high-
resistivity n-type silicon is analyzed, the recovery of the excess-
carrier lifetime as a function of annealing temperature above room
temperature will be investigated. In this ma:-m- er, the recombination
and trapping center may be associated with one of the known centers as
identified by ESR work. (4) Future plans call for the investigation of
the type of defects introduced in high-resistivity p-type silicon
irradiated with 30 MeV electrons at room temperature.
3. DC OONDUCTIVITY
Carrier lifetime expe ri.ments are being extended to include do
measurements. The circuitry being used has been described previously. (4)
The center responsible for the degradation of the lifetime had
been considered (2) to be deeper than 0,4 eV for n-type silicon samples
of carrier concentrations of 1015
 cm 3 . Presently we are using n-type
silicon samples of carrier concentrations of the order of 10 14 em 3.
In this way we hope to probe deeper into the energy gap and possibly
get into a region where the temperature dependence of the carrier lifetime
is exponential and thus obtain the defect energy level directly. Experi-
ments on p-type silicon samples will be similarly extended.
8
REFUMCES
1. V. A. J. van Lint, et al.,"Radiation Effects on Silicon So;Ar Cells,"
General Atomic Report GA-3872 (2/15/63) p. 61.
2. V. A. J. van Lint and D. P. Snowden, "Radiation Effects on Silicon
Solar Cells," General Atomic Report G L-6556 (7/21/65), p • 27•
3. H. Yoriye, et al., "Radiation Effects on Silicon," General Atomic
Report GACD-6249 (6/3x/66).
4. G. D. Watkins, Radiation Damage in Semiconductors, Academic Press,
P. 98, 1964.
9


Radiation effects on silicon Quarterly progress report, Oct. 1 - Dec. 31, 1966

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server