Analysis of dark currents and deep level traps in InP- and GaAs-based In0.83Ga0.17As photodetectors
Introduction
In recent decades, high indium (In) content InxGa1−xAs (0.53 < x < 1) photodetectors (PDs) with p-i-n InxGa1−xAs/InyAl1−yAs heterostructures have attracted much attention due to their important applications in environmental monitoring, earth observation, night vision, etc [1], [2], [3]. So far researchers have focused on demonstrating high indium content InxGa1−xAs PDs on InP substrate [4], but the performance of InxGa1−xAs PDs has been limited by the increased defect density in the absorbers due to an increase in the lattice mismatch. For instance, when x increases from 0.53 to 0.83 to move the cut-off wavelength from 1.7 to 2.5 μm, about +2.1% lattice mismatch with InP substrate will be introduced. Meanwhile, high indium content InxGa1−xAs PDs on GaAs substrate are also attractive since GaAs technology allows larger substrate sizes, so fabrication of larger size epitaxial wafers as well as larger format focal plane arrays (FPAs) would be realized [5], [6]. Nevertheless, the implementation of GaAs-based high indium content InxGa1−xAs PDs has been limited by the higher dark current due to increased defect density in the absorbers though a relatively thick continuously graded InAlAs buffer has been adopted in the structure [7], [8]. As well known that up to about 4% of extra lattice mismatch will be introduced in the system of InxGa1−xAs/GaAs with respect to the system of InxGa1−xAs/InP in case of the same In composition. This gives rise to undoubted increase in the densities of defects or traps in the forbidden gap, which can have important influences on the dark current degradation of PDs.
In order to explore the origin of the performance limiting mechanisms, as well as to suppress the dark current successfully in high indium InxGa1−xAs detectors, one helpful method is through the understanding of the properties of defects in the absorption layer. This will help to recognize the nature of the defect and make skillful design and growth of device quality wafers with reasonably good quality absorber layer in next step. In this paper, the temperature-dependent dark current characteristics of InP- and GaAs-based In0.83Ga0.17As PDs were compared. It was found that the component of tunneling current in the GaAs-based In0.83Ga0.17As PD dominates in a much larger temperature range with respect to that of InP-based In0.83Ga0.17As PD. Through comprehensive comparisons of deep level transient spectroscopies and non-radiative recombination processes, the high tunneling current in GaAs-based In0.83Ga0.17As PD was ascribed to a large number of deep traps in the absorber.
Section snippets
Experiments
Two PD wafers with In0.83Ga0.17As/In0.83Al0.17As p-i-n heterojunction structures were grown on (1 0 0)-oriented S-doped InP or GaAs epi-ready substrates by using a VG Semicon V80H gas source molecular beam epitaxy (GSMBE) system. Growth conditions were the same as our previous study [9]. The lattice mismatches between In0.83Ga0.17As absorption layer and substrate are about +5.9% and +2.1% for the GaAs and InP substrates, respectively. Each wafer consisted of a 2.55 μm N+ (N = 3 × 1018 cm−3) InAlAs
Results and discussions
Detailed material characteristics for both samples were described in Ref. [7]. Compared to the structure on InP, the In0.83Ga0.17As photodetector structure on GaAs shows relatively lower lattice quality with poorer surface morphology and broader full width at half maximum of X-ray diffraction, as well as weaker PL intensity. Roughly calculated from the cross-sectional transmission electron micrographs in Ref. [7], the dislocation density in the In0.83Ga0.17As absorption layer on GaAs is
Conclusion
In conclusion, we have investigated the temperature dependent dark current characteristics of In0.83Ga0.17As photodetectors grown on GaAs and InP substrates. At reverse bias of 10 mV, the dark current of GaAs-based PD is 2.28 μA at 300 K and 2.17 nA at 77 K, both significantly larger than that of 674 nA at 300 K and 3.99 pA at 77 K for InP-based PD. The component of tunneling current was found to be generated in a wider temperature range in the GaAs-based In0.83Ga0.17As PD with respect to that of
Acknowledgements
The authors wish to acknowledge the support of the National Key Research and Development Program of China under Grant No. 2016YFB0402400, the National Natural Science Foundation of China under grant Nos. 61405232, 61675225, and 61605232, and the Youth Innovation Promotion Association CAS under Grant No. 2013155.
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