The shortwave infrared(SWIR)waveband has traditionally been defined as the spectral region between 1 μm and 3 μm[
Journal of Infrared and Millimeter Waves, Volume. 42, Issue 5, 634(2023)
Study of Zinc-diffused InGaAs/InP planar infrared detector processed with rapid thermal annealing
The function of rapid thermal annealing on zinc-diffused In0.53Ga0.47As/InP PIN detector was systemically studied. By using electrochemical capacitance-voltage and secondary ion mass spectroscopy techniques, Zn and net acceptor concentration profiles were investigated, indicating that the annealing process would affect the dopant concentration but not affect the diffusion depth. In0.53Ga0.47As/InP PIN detectors under different annealing conditions were fabricated, the results showed that the detector without annealing process outperformed in terms of lower device capacitance and higher activation energy from 260 to 300K. By analyzing the mechanism of dark current, the unannealed sample exhibited lower Shockley-Read-Hall generation-recombination and diffusion currents, explaining the higher peak detectivity at room temperature. Therefore, for the purpose of fabricating high-performance planar InGaAs detectors with low-doped absorption layer, annealing process is inadvisable.
Introduction
The shortwave infrared(SWIR)waveband has traditionally been defined as the spectral region between 1 μm and 3 μm[
In recent years,SWIR detection systems are increasingly demanded for surveillance,reconnaissance,and remote sensing applications[
In this work,the function of rapid thermal annealing on zinc-diffused In0.53Ga0.47As/InP PIN detector was systemically studied. The pn junction in the InP/InGaAs heterostructure was prepared by sealed-ampoule Zn diffusion. The profiles of Zn and acceptor concentration before and after thermal annealing were investigated. By analyzing thermal activation energy and the mechanism of dark current,we explained lower dark current of the unannealed In0.53Ga0.47As/InP PIN detector.
1 Experiments
In experimental section,the n-i-n+ InP/InGaAs/InP epitaxy layers were grown on an n-type heavily doped InP substrate by metal-organic chemical vapor deposition(MOVCD)system. The epitaxial structure consisted of a 1 µm n-InP cap layer with electron concentration of 5×1016 cm-3,a 2.5 µm low-doped In0.53Ga0.47As absorption layer with electron concentration of 2×1014 cm-3 and a 1 µm highly Si-doped InP buffer layer with electron concentration of 2×1018 cm-3. The parameters of the as-prepared epitaxy material are given in
|
|
To form P-well in the cap layer,the Zn diffusion processes were implemented via sealed-ampoule technique. After diffusion,rapid thermal annealing treatment was performed on AccuThermo AW610 Rapid Thermal Processing System in N2 atmosphere. The variations of different annealing process are shown in
Figure 1.Cross-section diagram of the PIN planar type photodiode
Figure 2.The optical microscopy image of Φ1 mm detector
Zn diffusion depth was measured by electrochemical capacitance-voltage(ECV)depth profiling and by secondary ion mass spectroscopy(SIMS). In ECV characterization,a Schottky barrier is formed between the interface of semiconductor and an electrolyte,while capacitance-voltage measurements are used to determine the doping type and concentration. Carrier depth information is obtained by using calibrated anodization and dissolution[
The current-voltage(I-V)and capacitance-voltage(C-V)characteristics were measured by Agilent B1500A Semiconductor Device Analyzer. For the response characteristic,the blackbody response signal and total dark noise measurements were conducted by using a blackbody testing setup with a blackbody temperature of 900 K,a distance of 30 cm,and an aperture of 8 mm. Spectral responsivities were measured by using a Fourier spectrometer at RT.
2 Results and discussions
2.1 Zn diffusion profiles
Due to the limited characterization capability of SIMS and ECV on the micrometer-scale samples,sealed-ampoule diffusion was carried out on planar InP/InGaAs epitaxial wafer. Net acceptor concentration profiles were measured by the ECV technique as shown in
Figure 3.Net acceptor concentration profiles measured by ECV
Figure 4.Zn concentration profiles measured by SIMS
Moreover,the annealed sample exhibited more uniform Zn element distribution in InP cap layer as shown in
2.2 PL measurements
By using 532 nm laser,the laser continuously excites the electron-hole pairs in the InP cap layer,while the excited carriers are also continuously recombined to emit light. When the lifetime is long enough,the excited electron-hole pairs will be driven by concentration gradient to diffuse to the InGaAs layer,and then are recombined to emit light. By using 1064 nm laser,InP cap layer can not absorb the light in this band,since the incident light reach the InGaAs layer without loss in InP cap layer. The InSb near-infrared detector was adopted to detect the photoluminescence of the InGaAs layer,so 532 nm laser and 1064nm laser were actually applied to test the performance of the epitaxial layers and the InGaAs layer,respectively. PL spectrum at different laser wavelength were measured at RT,as shown in
Figure 5.PL spectrum of samples with different probe laser wavelengths:(a)only 532 nm probe;(b)only 1064 nm probe
2.3 Detector capacitance analysis
Reverse bias-dependent capacitances(Cd)of the photodiodes with and without rapid thermal annealing were characterized at RT,as shown in
Figure 6.Measured Cd-V curves of the unannealed PD and annealed PD
The capacitance density of the p+n abrupt junction can be represented by
Figure 7.The Cd-3-V curves and corresponding linear fitting curves of the unannealed PD and annealed PD
2.4 Dark current analysis
For photodetectors,dark current is the key parameter which must be decreased to improve signal to noise ratio and then minimize the noise equivalent power[
Dark current-voltage(I-V)measurements were carried out in a cryogenic probe station which was connected to a precision semiconductor parameter analyzer and also precisely controlled the chamber temperature.
Figure 8.Measured dark currents for Φ1 mm detectors with different annealing time raging form 260K to 300K:(a)260K;(b)270K;(c)280K;(d)290K;(e)300K
Dark current mechanisms are dominated by diffusion current when Ea= Eg,whereas dominated by SRH generation-recombination current and shunt current when Ea= Eg/2. The energy bandgap Eg of In0.53Ga0.47As is 0.735eV at 300 K. In the following discussion,the weak energy bandgap change with temperature is ignored. Arrhenius plots of the temperature-dependent dark currents at different reverse-bias voltages for the unannealed PD and the annealed PD were shown in
Figure 9.The dark current density as a function of 1000/T at different reverse-bias voltage for Φ1 mm detectors of different annealing time:(a)annealing 0 min;(b)annealing 10 minTable 3 The thermal activation energy Ea of the unannealed PD and the annealed PD
|
At 260-300 K,the Ea of the unannealed PD was constantly higher than that of the annealed PD at different reverse-bias voltages,which indicates that non-diffusion current accounts for a larger proportion for the annealed PD. Also,the Ea gradually decreased for both PDs as reverse bias voltage increased. Since diffusion current is solely saturate at relatively high reverse bias,SRH generation-recombination current increases with the widened depleted region.
The dark currents measured and fitted for the unannealed PD and the annealed PD at 300K were showed in
Figure 10.Dark current measured at 300K and fitted for Φ1 mm detectors of different annealing time:(a)annealing 0 min;(b)annealing 10 min
2.5 Spectral response and peak detectivity
To analyze the impacts of the rapid thermal annealing on photoelectric detection,spectral response and detectivity were also investigated. The as-prepared separate detectors with different annealing conditions were packaged in Dewars for the measurement. The spectral response of the detectors was carried out by a Fourier transform infrared spectrometer at room temperature under zero bias as seen in
Figure 11.The detectivity spectrum of detectors at 300K
Peak wavelength detectivity(D*)represents the sensitivity of the photosensitive element of the detector under unit bandwidth area and per unit radiation power. The RT response signal and dark noises under zero bias were also acquired by using a lock-in amplifier with a ×108 voltage preamplifier under a 900 K blackbody radiation chopped at 800 Hz,from which the peak D* were deduced. The calculated peak detectivity of the unannealed detector is 6.2×1012 cmHz1/2W-1,obviously higher than the annealed detector with the value of 5.7×1012 cmHz1/2W-1 at RT. Such results clearly proved that the unnecessity of rapid thermal annealing treatment for the InGaAs/InP PIN detector with low-doped absorption layer.
3 Conclusions
In this work,the function of rapid thermal annealing on In0.53Ga0.47As/InP PIN detector with low-doped absorption layer was investigated. The results of SIMS and ECV showed that the dopant accumulation around the InGaAs/InP junction region was directly affected by annealing after Zn diffusion. The capacitance-voltage measurement revealed that impurity concentration distribution of the linearly graded junction in InGaAs layer and the lower capacitance of the unannealed detector. Moreover,the unannealed detectors has a lower dark current in the full temperature range,benefiting from the suppressed dopant accumulation. The fitting results indicated the annealed detector has higher SRH current and diffusion current. The peak detectivity of the unannealed detector is 6.2×1012 cmHz1/2W-1,8.8% higher than that of the annealed sample. Therefore,for the purpose of fabricating high-performance planar InGaAs detectors with low-doped absorption layer,annealing process is inadvisable.
[11] Yin Hao, Li Yong-Fu, Wang Wen-Juan et al. Scanning capacitance microscopy characterization on diffused p-n junctions of InGaAs/InP infrared detectors[J]. Proc SPIE, 7658, 237-238(2010).
[15] Cao Gao-Qi. Study on high sensitivity planar InGaAs short wavelength infrared detector[D](2016).
[19] Gurp G V, Boudewijn P R, Kempeners M et al. Zinc diffusion in n‐type indium phosphide[J]. Journal of Applied Physics, 61, 1846-1855(1987).
[22] Liu E K, Zhu B S, Luo J S et al[M]. The Physics of Semiconductors(2003).
Get Citation
Copy Citation Text
Jia-Sheng CAO, Tao LI, Yi-Zhen YU, Chun-Lei YU, Bo YANG, Ying-Jie MA, Xiu-Mei SHAO, Xue LI, Hai-Mei GONG. Study of Zinc-diffused InGaAs/InP planar infrared detector processed with rapid thermal annealing[J]. Journal of Infrared and Millimeter Waves, 2023, 42(5): 634
Category: Research Articles
Received: Dec. 15, 2022
Accepted: --
Published Online: Aug. 30, 2023
The Author Email: Tao LI (litao@mail.sitp.ac.cn), Hai-Mei GONG (hmgong@mail.sitp.ac.cn)