Ge/Si heterojunction photodetector for 1.064 μm laser pulses
Iso- and anisotype heterojunction Ge/Si photodetectors were made by depositing Ge layer onto monocrystalline Si using a vacuum evaporation technique. These detectors before and after annealing were utilized to detect 1.064 µm Nd:YAG laser pulses. The study also included determination of the optimal...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Zitieren: | Ge/Si heterojunction photodetector for 1.064 μm laser pulses / Raid A. Ismail, Jospen Koshapa, Omar A. Abdulrazaq // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 49-52. — Бібліогр.: 11 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1214332025-02-09T10:22:58Z Ge/Si heterojunction photodetector for 1.064 μm laser pulses Ismail, Raid A. Koshapa, Jospen Abdulrazaq, Omar A. Iso- and anisotype heterojunction Ge/Si photodetectors were made by depositing Ge layer onto monocrystalline Si using a vacuum evaporation technique. These detectors before and after annealing were utilized to detect 1.064 µm Nd:YAG laser pulses. The study also included determination of the optimal Ge thickness and annealing conditions. The experimental results show that the photoresponse was highly improved after classical thermal annealing and rapid thermal annealing (RTA). The voltage responsivity and signal rise time results strongly depended on the annealing type and conditions. It was found that the optimal conditions can be obtained for n-Ge/p-Si photodetector prepared with Ge 200 nm thick and treated with RTA at 500 ºC for 25 s. 2006 Article Ge/Si heterojunction photodetector for 1.064 μm laser pulses / Raid A. Ismail, Jospen Koshapa, Omar A. Abdulrazaq // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 49-52. — Бібліогр.: 11 назв. — англ. 1560-8034 PACS 42.79.Pw, 85.60.Gz https://nasplib.isofts.kiev.ua/handle/123456789/121433 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Iso- and anisotype heterojunction Ge/Si photodetectors were made by depositing Ge layer onto monocrystalline Si using a vacuum evaporation technique. These detectors before and after annealing were utilized to detect 1.064 µm Nd:YAG laser pulses. The study also included determination of the optimal Ge thickness and annealing conditions. The experimental results show that the photoresponse was highly improved after classical thermal annealing and rapid thermal annealing (RTA). The voltage responsivity and signal rise time results strongly depended on the annealing type and conditions. It was found that the optimal conditions can be obtained for n-Ge/p-Si photodetector prepared with Ge 200 nm thick and treated with RTA at 500 ºC for 25 s. |
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Ismail, Raid A. Koshapa, Jospen Abdulrazaq, Omar A. |
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Ismail, Raid A. Koshapa, Jospen Abdulrazaq, Omar A. Ge/Si heterojunction photodetector for 1.064 μm laser pulses Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Ismail, Raid A. Koshapa, Jospen Abdulrazaq, Omar A. |
| author_sort |
Ismail, Raid A. |
| title |
Ge/Si heterojunction photodetector for 1.064 μm laser pulses |
| title_short |
Ge/Si heterojunction photodetector for 1.064 μm laser pulses |
| title_full |
Ge/Si heterojunction photodetector for 1.064 μm laser pulses |
| title_fullStr |
Ge/Si heterojunction photodetector for 1.064 μm laser pulses |
| title_full_unstemmed |
Ge/Si heterojunction photodetector for 1.064 μm laser pulses |
| title_sort |
ge/si heterojunction photodetector for 1.064 μm laser pulses |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2006 |
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https://nasplib.isofts.kiev.ua/handle/123456789/121433 |
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Ge/Si heterojunction photodetector for 1.064 μm laser pulses / Raid A. Ismail, Jospen Koshapa, Omar A. Abdulrazaq // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 49-52. — Бібліогр.: 11 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT ismailraida gesiheterojunctionphotodetectorfor1064mmlaserpulses AT koshapajospen gesiheterojunctionphotodetectorfor1064mmlaserpulses AT abdulrazaqomara gesiheterojunctionphotodetectorfor1064mmlaserpulses |
| first_indexed |
2025-11-25T20:30:44Z |
| last_indexed |
2025-11-25T20:30:44Z |
| _version_ |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 49-52.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
49
PACS 42.79.Pw, 85.60.Gz
Ge/Si heterojunction photodetector for 1.064 μm laser pulses
Raid A. Ismail1*, Jospen Koshapa2, Omar A. Abdulrazaq3
1Applied Physics Center, Ministry of Science and Technology, Baghdad, Iraq
E-mail: raidismail@yahoo.com
*Present address: Faculty of education, Hadrhamout University, Yemen
2Applied Science Dept., University of Technology, Baghdad, Iraq
3NASSR State Company, Ministry of Industry and Minerals
Abstract. Iso- and anisotype heterojunction Ge/Si photodetectors were made by
depositing Ge layer onto monocrystalline Si using a vacuum evaporation technique.
These detectors before and after annealing were utilized to detect 1.064 µm Nd:YAG
laser pulses. The study also included determination of the optimal Ge thickness and
annealing conditions. The experimental results show that the photoresponse was highly
improved after classical thermal annealing and rapid thermal annealing (RTA). The
voltage responsivity and signal rise time results strongly depended on the annealing type
and conditions. It was found that the optimal conditions can be obtained for n-Ge/p-Si
photodetector prepared with Ge 200 nm thick and treated with RTA at 500 ºC for 25 s.
Keywords: Ge/Si photodetector, thermal annealing, Nd:YAG laser pulse.
Manuscript received 24.01.06; accepted for publication 29.03.06.
1. Introduction
The wide use of Nd:YAG laser in industrial, medical,
and military applications has initiated extensive
researches on photon detectors for the wavelength
1.064 μm [1-4]. Nowadays, fabrication of IR-detectors is
directed principally towards heterojunction photo-
detectors. The fabrication simplicity and absence of
high-temperature diffusion processes were an incentive
to use a heterojunction as IR-detector. Ge/Si
heterojunction is an appropriate junction for detectors in
the visible and IR ranges 500 to 1800 nm [2, 5-6]. The
high mismatch (about 4.2 %) takes place between Ge
and Si would degrade the detector properties. Many
studies were devoted to reduce the mismatch effect by
varying the Ge layer thickness when using GexSi1-x [6]
and Ge1-xCx layers [7] as well as by post-deposition
thermal annealing [8]. Previous study on the Ge/Si
heterojunction was centered on its optoelectronics
properties after and before annealing [9]. In this study,
the effect of the Ge-layer thickness and annealing
conditions (involving classical thermal annealing (CTA)
and rapid thermal annealing (RTA) techniques) on Ge/Si
photodetector main parameters for 1.064 µm laser pulses
were described.
2. Experimental procedure
High purity germanium (99.99 %) was deposited on
(111)-oriented monocrystalline silicon wafers of n- and
p-type conductivity and 3…5 Ohm·cm resistivity using
the thermal resistive technique (pressure in vacuum
chamber was less than 10-6 Torr). The thickness of the
Ge layer varied from 50 to 250 nm at 50-nm intervals.
As ohmic contacts, Al and Sn were deposited onto Si
and Ge, respectively. Photoresponse of the detectors
(Ge-side) was measured by exposure to the 400 μs single
pulse of Nd:YAG laser, and the output voltage signal
was recorded across a load resistance of 5 kOhm
connected in series with the reverse biased detector and
monitored by storage oscilloscope (100 MHz). In a tube
furnace, CTA was performed at various temperatures
200 to 600 °C for 30 min, while RTA was made by
utilizing incoherent light from a halogen lamp (one sided
illumination mode) at temperatures 200 to 600 °C for
25 s. The set-up of RTA system is schematically shown
in Fig. 1. Four-point probe measurement was used to
investigate the conductivity type of the Ge deposited
layer. The signal rise time of photodetectors was
measured using 2 ns (FWHM) diode pumped Nd:YAG
laser pulses formed with the aid of 300 MHz CRO.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 49-52.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
50
Quartz Tube
Sample
Valve
Rotary Pump
Thermocouple Reader
Stand
Halogen Lamp
Fig. 1. Scheme of RTA system.
3. Results and discussion
Using the four-probe technique, it was revealed that the
type of conductivity of Ge layers is n-one, thereby, it is
anticipated that the anisotype heterojunction can be
formed by depositing the Ge-layer onto p-Si substrate,
while the deposition of Ge-layer onto n-Si substrate will
form an anisotype heterojunction. The voltage
responsivity of photodetectors to Nd:YAG laser pulses
versus the reverse bias voltage for variuos thicknesses is
given in Fig. 2. It is obvious that the responsivity to the
wavelength 1.064 μm increases with reverse bias
voltage. This can be accounted for definetely by the
increase in the depletion region width with the reverse
bias, and hence most of generated carriers will be
accumulated near the junction. The observed saturation
refers to full accumulation in the space charge region
and may take place due to increasing the noise voltage of
detector at high-voltage biases. Moreover, it can be seen
that the photoresponse increases with increase of the
thickness up to 200 nm and then decreased clearly. This
observation may be interpreted by the reduction of the
resistance in series with increasing the thickness in
addition to the location of the depletion region far from
the surface, which in turns reduces the surface
recombination. While in the case of the large thickness
(more than 200 nm) the role of dislocations will be
significant due to lattice mismatch and will negatively
affects the device operation. Furthermore, the anisotype
n-Ge/p-Si heterojunction detector exhibits better results
than the isotype n-Ge/n-Si one, which is in a full
agreement with published results.
Results of treating the photodetector by CTA for
the anisotype Ge/Si detector with the Ge-layer thickness
of 200 nm and the annealing time 20 min are shown in
Fig. 3. It is obvious that the detector properties are
enhanced with increase of the annealing temperature (up
to 500 °C). This enhancement is probably ascribed to the
reduction in structural defect density of the Ge-layer
[10]. An annealing cycle with the high temperature
Ta > 500 °C degrades the detector characteristics because
of the effects occuring at the interface and bulk
properties as well as those caused by nondesirable
diffusion of Si into Ge at the interface [11].
0
1
2
3
4
5
6
7
0 2 4 6 8 10 12 14
Reverse voltage (V)
R
es
po
ns
iv
ity
×
1
03 (V
/W
)
50 nm
250 nm
100 nm
150 nm
200 nm
a
0
1
2
3
4
5
0 2 4 6 8 10 12 14
Reverse voltage (V)
R
es
po
ns
iv
ity
×
1
03 (V
/W
)
50 nm
250 nm
100 nm
150 nm
200 nm
b
Fig. 2. The variation of voltage responsivity with the reverse
bias voltage for various Ge-layer thicknesses: anisotype (a) and
isotype (b) n-Ge/n-Si heterojunction detectors.
Fig. 4 depicts the influence of RTA on n-Ge/p-Si
responsivity with Ge-layer thickness of 200 nm and
annealing time of 25 s. The figure shows that this
responsivity increases remarkedly after RTA compared
with that for unannealed detectors. The photodetector
annealed at 500 °C/25 s gave best results, and further
increase in the temperature annealing results in
decreasing the voltage responsivity. This can be ascribed
to excess of Si diffusion into Ge since the activation
energy of Ge is higher than that of Si [8]. On the other
hand, the beneficial effect of post-annealing on the
electrical and structrural properties of Ge epilayers on
the detector operation has resulted from the decrease of
threading the dislocation densities [11].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 49-52.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
51
Fig. 3. n-Ge/p-Si photodetector (200 nm thick Ge) voltage
response for Nd:YAG laser at the various CTA temperatures.
Fig. 5 shows a laser pulse recorded by unannealed
and annealed photodetectors. It is obvious that the
annealed samples show higher response than the
unannealed ones. When the incident laser pulse power
increases, the detector output voltage will be increased
as shown in Fig. 6. The figure illustrates that at a high
power a saturation region did not appear. From this
curve, linearity deviation K was calculated and
approximately equals to 10 % for unannealed samples
and 6 % for the annealed ones.The time analysis shows
that the optimal annealed photodetector gave the rise
time close to 18 ns and the other photodetectors
exhibited the rise time ranging between 75 and 90 ns
depending on preparation conditions. The previous
measurements were repeated after six months and no
remarkable degredation was observed.
Fig. 4. Anisotype photodetector response for Nd:YAG laser at
the various RTA temperatures.
a
b
Fig. 5. Photographs of laser waveform recorded by detectors
with the Ge-layer thickness of 200 nm and at 20 V reverse bias
before annealing (a) and after RTA (b) at 500 ºC and 25 s.
(Hor. ms/div), (Ver. V/div).
2
4
6
0,8 1,2 1,6 2 2,4
Power (mW)
O
ut
pu
t v
ol
ta
ge
(V
)
Fig. 6. Linearity characteristics of the best photodetector
for Nd:YAG laser.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 49-52.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
52
4. Conclusions
Demonstrated were p-n- and p-p-photodetectors capable
to register Nd:YAG laser pulses and made from
heterojunctions of p-type Ge epilayers on n- and p-type
Si substrates without using a buffer interface layer and
without anti-reflection coating. The detecton ability for
Nd:YAG laser pulses were investigated as a function of
Ge thickness and annealing conditions. Post-annealing
of these photodetectors leads to a significant
improvement in their important characteristics, namely,
voltage responsivity, linear characteristics, and rise time.
The photodetector treated by RTA (500 °C/25 s)
demonstrates superiour detection properties comparing
to conventional p-n and p-i-n silicon homojunction
photodetectors. These photodetectors exhibits a good
stability of their characteristics.
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