Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24340 AlxIn1-x As ysb1-y photodiodes with low avalanche breakdown temperature dependence ANDREW H. JONES,1 YUAN YUAN,1 MIN REN,1 SCOTT J. MADDOX,2 SETH R. BANK,2 AND JOE C. CAMPBELL1 1 Electrical and Computer Engineering Department, University of Virginia, 351 McCormick Rd. Charlottesville, VA 22904, USA 2 Electrical and Computer Engineering Department, University of Texas at Austin, 1616 Guadalupe St. Austin, TX 78758, USA Abstract: We report AlxIn1-xAsySb1-y PIN and Separate Absorption, Charge and Multiplication (SACM) avalanche photodiodes (APDs) with high temperature stability. This work is based on measurements of avalanche breakdown voltage of these devices for temperatures between 223 K and 363 K. Breakdown voltage temperature coefficients are shown to be lower than those of APDs fabricated with other materials with comparable multiplication layer thicknesses. 2017 Optical Society of America OCIS codes: (040.1345) Avalanche photodiodes (APDs); (040.5160) Photodetectors; (060.2360) Fiber optics links and subsystems; (120.6810) Thermal effects. References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. J. C. Campbell, Recent Advances in Avalanche Photodiodes, J. Lightwave Technol. 34(2), 278 285 (2016). L. J. J. Tan, D. S. G. Ong, J. S. Ng, C. H. Tan, S. K. Jones, Y. Qian, and J. P. R. David, Temperature Dependence of Avalanche Breakdown in InP and InAlAs, IEEE J. Quantum Electron. 46(8), 1153 1157 (2010). D. J. Massey, J. P. R. David, and G. J. Rees, Temperature Dependence of Impact Ionization in Submicrometer Silicon Devices, IEEE Trans. Electron Dev. 53(9), 2328 2334 (2006). N. Susa, H. Nakagome, O. Mikami, H. Ando, and H. Kanbe, New InGaAs/InP avalanche photodiode structure for the 1-1.6 µm wavelength region, IEEE J. Quantum Electron. 16(8), 864 870 (1980). X. Zhou, C. H. Tan, S. Zhang, M. Moreno, S. Xie, S. Abdullah, and J. S. Ng, Thin Al1-x Ga x As0.56Sb0.44 Diodes with Extremely Weak Temperature Dependence of Avalanche Breakdown, R. Soc. Open Sci. 4(5), 170071 (2017). M. E. Woodson, M. Ren, S. J. Maddox, Y. Chen, S. R. Bank, and J. C. Campbell, Low-noise AlInAsSb Avalanche Photodiode, Appl. Phys. Lett. 108(8), 081102 (2016). M. Ren, S. J. Maddox, Y. Chen, M. Woodson, J. C. Campbell, and S. R. Bank, AlInAsSb/GaSb Staircase Avalanche Photodiode, Appl. Phys. Lett. 108(8), 081101 (2016). M. Ren, S. J. Maddox, M. E. Woodson, Y. Chen, S. R. Bank, and J. C. Campbell, AlInAsSb Separate Absorption, Charge, and Multiplication Avalanche Photodiodes, Appl. Phys. Lett. 108(19), 191108 (2016). M. Ren, S. J. Maddox, M. E. Woodson, Y. Chen, S. R. Bank, and J. C. Campbell, Characteristics of AlxIn1 xasysb1-y (x:0.3 0.7) Avalanche Photodiodes, J. Lightwave Technol. 35(12), 2380 2384 (2017). S. J. Maddox, S. D. March, and S. R. Bank, Broadly Tunable AlInAsSb Digital Alloys Grown on GaSb, Cryst. Growth Des. 16(7), 3582 3586 (2016). H. Liu, H. Pan, C. Hu, D. McIntosh, Z. Lu, J. C. Campbell, Y. Kang, and M. Morse, Avalanche Photodiode Punch-through Gain Determination Through Excess Noise Analysis, J. Appl. Phys. 106(6), 064507 (2009). K. Hyun and C. Park, Breakdown Characteristics in InP/InGaAs Avalanche Photodiode with p-i-n Multiplication Layer Structure, J. Appl. Phys. 81(2), 974 984 (1997). R. Sidhu, L. Zhang, N. Tan, N. Duan, J. C. Campbell, A. L. Holmes, Jr., C.-F. Hsu, and M. A. Itzler, 2.4 μm Cutoff Wavelength Avalanche Photodiode on InP Substrate, Electron. Lett. 42(3), 181 182 (2006). A. Rouvie, D. Carpentier, N. Lagay, J. Decobert, F. Pommereau, and M. Achouche, High Gain Bandwidth Product Over 140-GHz Planar Junction AlInAs Avalanche Photodiodes, IEEE Photonics Technol. Lett. 20(6), 455 457 (2008). Y. L. Goh, D. S. Ong, S. Zhang, J. S. Ng, C. H. Tan, and J. P. R. David, InAlAs Avalanche Photodiode with Type-II Absorber for Detections beyond 2 μm, Proc. SPIE 7398, 729837 (2009). #304745 Journal 2017 https://doi.org/10.1364/oe.25.024340 Received 14 Aug 2017; revised 14 Sep 2017; accepted 16 Sep 2017; published 25 Sep 2017
Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24341 1. Introduction Avalanche photodiodes have been widely used in telecommunication, military, and research applications requiring receivers with high optical sensitivity [1]. APDs typically exhibit a proportional relationship between ambient temperature and bias required to maintain a constant gain, M. This is due to a change in impact ionization efficiency with temperature. Phonon scattering increases with temperature, necessitating a higher electric field and hence a higher reverse bias to realize a given avalanche gain. This gain-temperature relationship can be extended to the variation of breakdown voltage with temperature and is characterized by the breakdown voltage temperature coefficient ΔVbd/ΔT [2]. APDs operated in Geiger mode, which is used for single photon detection, are even more susceptible to slight variations in temperature. As a result of this dependence, complex cooling circuits are required to maintain a constant gain. APDs requiring only simple bias feedback circuits due to minimal values of ΔVbd/ΔT are desirable for such highly sensitive applications. Another factor contributing to ΔVbd/ΔT is the APD multiplication layer thickness. It has been shown that as the thickness of this layer increases, ΔVbd/ΔT increases linearly for temperatures between 200~400 K, while at lower temperatures, ΔVbd/ΔT is minimized [2,3]. InP and AlInAs APDs are widely used due to their low dark current and compatibility with near-infrared fiber optic telecommunications links [4]. Si APDs are also widely used for their low noise characteristics and compatibility with high-speed integrated circuitry. Extensive studies have categorized the temperature dependence of APDs designed in these material systems [2,3]. Recently, thin Al 1-x Ga x As y Sb 1-y APDs, which are lattice matched to InP, were reported with exceptionally low ΔVbd/ΔT values [5]. Previously reported Al x In 1-x As y Sb 1-y PIN and SACM APDs, which are lattice matched to GaSb, have demonstrated low excess noise, k = 0.01~0.05, and high absorption efficiency covering a wide optical spectrum [6 9]. In this paper we report temperature-dependent studies of these Al x In 1-x As y Sb 1-y APDs. In order to further test the robustness of these APDs, temporal stability was also measured. 2. Experimental details 2.1 Device growth and fabrication Al x In 1-x As y Sb 1-y epitaxial layers, with Al concentration from x = 0.3-0.7, were grown on n- type Te-doped GaSb (001) substrates by solid-source molecular beam epitaxy (MBE) as digital alloys of the binary semiconductors [10]. Two Al x In 1-x As y Sb 1-y PIN APDs with x = 0.6 and 0.7, and an Al x In 1-x As y Sb 1-y SACM APD were studied. The PIN and SACM APDs had multiplication layer thicknesses of 890nm and 1μm, respectively. The structural cross sections of the devices are shown in Fig. 1. Refs [6 9]. describe the APD structures in greater detail. Circular mesas were defined by standard photolithography techniques and N 2 /Cl 2 inductively coupled plasma dry etching. A bromine-methanol treatment was used to remove surface damage, and the mesa sidewalls were passivated with SU-8 to reduce surface leakage current. Ti/Pt/Au ohmic contacts were deposited using electron-beam evaporation. 2.2 Device growth and fabrication The APDs under test were placed in a nitrogen-cooled cryogenic chamber in order to precisely control ambient temperature. A 543 nm He-Ne CW laser was coupled into the chamber via a 9 μm-core lensed fiber in order to achieve single-carrier electron injection into the high-field multiplication regions of the APDs. Current-voltage characteristics of the APDs under test were measured with an HP 4148 semiconductor parameter analyzer. The gain, M, of the PIN APDs was extracted directly from the measured photocurrent, whereas M of the SACM APDs was determined by fitting photocurrent and excess noise [11]. The breakdown voltage of the APDs was determined by extrapolating the inverse gain 1/M to zero. ΔV bd /ΔT
Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24342 was determined by measuring the variation of the breakdown voltage from 223 to 363 K and applying a linear fit. The temporal stability of the gain was measured by illuminating the devices with a 543 nm He-Ne CW laser. At room temperature (300 K), a gain of M = 10 was set for both x = 0.6 and x = 0.7 PIN APDs, while a gain of M = 13 was set for the SACM APDs. The photocurrent of each device was continuously measured for two hours. Fig. 1. Structural cross section of Al x In 1-x As y Sb 1-y PIN APDs (left) and SACM APD (right). 3. Results Figure 2 shows the breakdown voltages of the APDs as a function of ambient temperature. The slope of the linear curve fit represents ΔVbd/ΔT. The values for the Al x In 1-x As y Sb 1-y x = 0.6 and 0.7 PIN APDs and the SACM APD are 2.5, 3.8, and 15.8 mv/k, respectively. Ref [9]. contains gain curves indicating that tunneling effects are not a factor when these devices are operated at high bias. Fig. 2. Breakdown voltages of Al x In 1-x As y Sb 1-y APDs as a function of temperature.
Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24343 Figure 3 shows the relation of ΔV bd /ΔT to multiplication layer thickness for both PIN and SAM APDs. Included in the comparison with Al x In 1-x As y Sb 1-y are InP, AlInAs, Si, and Al 1- xga x As y Sb 1-y [2,3,5]. Ref [2]. reports a linear relation between ΔV bd /ΔT and multiplication layer thickness, which can be represented by simple linear equations for InP and AlInAs devices. Furthermore, these equations can be scaled for SAM APDs by accounting for the depletion width [2]. These linear curves are included in Fig. 3, where the depletion width is assumed to be 1 μm larger than the multiplication layer thickness, similar to the data found in [2]. Fig. 3. ΔV bd /ΔT as a function of multiplication layer thickness for PIN APDs (a) and SAM APDs (b). Values of ΔVbd/ΔT for the Al x In 1-x As y Sb 1-y PIN and SACM APDs are shown in Table 1 and compared with InP, AlInAs, Si, and Al 1-x Ga x As y Sb 1-y APDs of various multiplication
Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24344 layer thicknesses. When compared to devices with similar multiplication layer thicknesses, ΔVbd/ΔT of Al x In 1-x As y Sb 1-y PIN APDs is less than a quarter that of AlInAs devices and almost an order of magnitude lower than ΔVbd/ΔT for InP and Si devices. ΔVbd/ΔT for Al x In 1- xas y Sb 1-y SACM APDs is less than half that of AlInAs SAM structures and less than a quarter of ΔVbd/ΔT for InP SAM structures with similar multiplication layer thicknesses. Al x In 1- xas y Sb 1-y PIN APDs only show values of ΔVbd/ΔT approximately three times higher than Al 1- xga x As y Sb 1-y devices ([5]), which have multiplication layer thicknesses almost eight times thinner. Table 1. Summary of experimental breakdown voltage temperature coefficient for APDs of various materials and multiplication layer thicknesses. Material & Structure Mult. Layer Thickness (μm) ΔV bd /ΔT (mv/k) Al 0.6 In 1-0.4 As y Sb 1-y PIN 0.89 2.5 Al 0.7 In 1-0.3 As y Sb 1-y PIN 0.89 3.8 0.8 35 InP PIN [2] 0.55 24 0.13 6 1 16 AlInAs PIN [2] 0.5 8.7 0.1 2.5 Si PIN [3] 0.8 21.15 Al 1-x Ga x As y Sb 1-y PIN [5] 0.11-0.116 0.86-1.08 Al x In 1-x As y Sb 1-y SACM 1 15.8 InP SAM [13] 0.8 100 InP SAM [12] 0.4 70 InP SAM [2] 0.2 46 AlInAs SAM [15] 1 40 AlInAs SAM [14] 0.2 25 AlInAs SAM [2] 0.15 23 Figure 4 shows the stability of Al x In 1-x As y Sb 1-y APD gain as a function of time. Within a two-hour period, the PIN APDs demonstrated maximum gain errors of 1.7% and 5.1% for x = 0.6 and x = 0.7 devices respectively. In the same test, the SACM APDs demonstrated a maximum gain error of 7.4%. Fig. 4. Multiplication gain of Al x In 1-x As y Sb 1-y APDs as a function of time at 300 K. PIN APDs were operated with a bias corresponding to a gain of 10 and SACM APDs were operated with a bias corresponding to a gain of 13.
Vol. 25, No. 20 2 Oct 2017 OPTICS EXPRESS 24345 4. Conclusion Studies with Al x In 1-x As y Sb 1-y APDs over a wide range of ambient temperatures show superior ΔVbd/ΔT compared to APDs of conventional materials. Both PIN and SACM APD structures have demonstrated robust performance amid temperature fluctuations. Temporal measurements also indicate high stability. Combined with the previously reported low noise, low k, and high absorption efficiency characteristics of these devices, Al x In 1-x As y Sb 1-y APDs offer the possibility of high-performance over a wide range of operating temperatures. Funding Defense Advanced Research Projects Agency (DARPA); Army Research Office (ARO).