Abstract
In this dissertation, we report on the design of large-area planar InP/InGaAs/InP heterostructure p-i-n photodiodes (PIN-PDs) with various antireflective layer structures and double-path reflectors for the enhancement in the position sensitivity, device response, and quantum efficiency. The antireflection (AR) coating structure is composed of high and low refractive index materials, including the insulating type of SiO2/Si3N4 bi-layer, conducting type of SiO2/GZO bi-layer, and conducting type of SiO2/GZO/NiOx tri-layer. The double-path reflector consists of AuGe-based alloys. The thermal-mode ALD (TM-ALD), plasma-mode ALD (PM-ALD), and radio-frequency (RF) sputtering methods were employed to deposit the n-type conductivity of GZO films. For ALD technology, a sandwich structure of GZO films was accomplished by layer-by-layer growth method. The performance of GZO films can be improved by modulating the growth temperature and introducing various oxygen sources. ALD-GZO films exhibit a resistivity of 3.8 x 10-3 Ω-cm, carrier concentration of 3.4 x 1020 cm-3, average optical transmittance of above 90% in the visible and infrared regions. For RF-sputtering, GZO films exhibit the resistivity of 2.9 x 10-3 Ω-cm and carrier concentration of 3.6 x 1020 cm-3. However, the optical transmittance is too low to be used for the infrared regions. On the other hand, the p-type conductivity of NiOx film can be fabricated by both e-beam evaporation and RTA process in oxygen ambient. Thus, the heavily GZO films (＞1020 cm-3) with low resistivity (~10-3 Ω-cm) were deposited onto the p-InP/InGaAs structure by both RF sputtering and PM-ALD, which always reveal a Schottky contact characteristics. The barrier height improvement at the n-GZO/p-InP interface is proposed by using the dual zinc driven-in steps and a NiOx insertion layer to realize the ohmic characteristics. The high zinc concentration (5-8 × 1018 cm-3) is first obtained in the surface of p-InP cap layer via the dual zinc driven-in steps. An array of transmission line method (TLM) structures were designed and constructed on top of the p-InP cap layer for the contact performance. The barrier height plays an important role for the formation of ohmic property between n-type GZO and p-type InP using NiOx insertion. By inserting a NiOx layer between GZO and Au/Cr contact films, the Au/Cr/GZO/NiOx contact pad for zinc driven-in p-InP cap layer exhibits a good ohmic contact behavior and a low specific contact resistance of 3.07 × 10-4 Ω-cm2 with the post-annealing process of 430℃ for 180 sec. Thus, the transparent conducting Ga-doped ZnO (GZO) layer was grown on top of the InGaAs PIN-PDs by PM-ALD to improve in the lateral resistance effect, and the NiOx layer was used to reduce the barrier height between n-GZO and p-InP. The SiO2/GZO/NiOx antireflection shows an average optical transmittance of above 90% and reflectance of below 10% in the infrared spectrum. The AuGe/Au backside reflector presents the optical reflectance of above 80%. Then, the combination of two features of antireflection coating and double-path reflector is employed to decrease incident-light loss and increase double-path absorption. By introducing both the transparent-conducting-based AR coating and double-path reflectors into the device structure, the large-area planar InGaAs PIN-PDs exhibit a low dark current density of 32.8 nA/cm2 at 5-V reverse bias, a high breakdown voltage of 35-V reverse bias, high build-in voltage of 1.65 eV, high responsivity of 0.93 A/W at 1310 nm and 1.09 A/W at 1550 nm, and a high quantum efficiency of near 90% in the 1000-1600 nm spectral range. The cutoff wavelength is obtained to be about 1650 nm. Under the high-power light illumination, the photosensitivity profile of position information of InGaAs-based PD with SiO2/GZO/NiOx AR coating tri-layer is uniform and instantaneous distribution.