Fabrication And Study Of InGaAs/InP Single Photon Avalanche Photodiodes(APDs)

Based on the fast-growing demands for the near-infrared (1550nm) single photon detection, this paper mainly concerned on the relevant research of the Separate Absorption, Grading, Charge, Multiplication (SAGCM) InGaAs/InP avalanche photodiodes (APDs). We fabricated the InGaAs/InP APDs after the device processes optimization, and we analysis theoretically the measurement results of the APDs through TCAD simulation. Details are as follows:1. The effects of the structural parameters of the charge layer and multiplication layer on the performance of the APDs are studied. The breakdown voltage(Vb) of the APDs decreases linearly (40V/1E12cm-2) with the increasing of the charge density in the charge layer, while the punch-through voltage (Vp) rises linearly and slowly(4V/1E12cm-2) at the same time. The charge layer influences the Vb and Vp by adjusting the electric field distribution between the absorption layer and multiplication layer. However, the Vb is decreases rapidly at first and then increases slowly with the increasing of the thickness of the multiplication layer, which is caused by the influence of the electric field and the impact ionization in the multiplication layer. These results are the basis for the device design.2. The p-type InP doping with thermal Zn diffusion are studied by the means of SCM, SIMS, ECV. The results shows that the concentration of holes is lower than the concentration of Zn atoms, and a Zn accumulation layer is formed near the InP surface, which will affect the p-type InP Ohmic electrode contact and increase the contact resistance. A better Ohmic electrode contact even without annealing process is obtained after removing the Zn accumulation layer. And for the500℃diffusion,450℃,1min rapid thermal annealing will affect the diffusion depth.3. We fabricated successfully the SAGCM InGaAs/InP APDs with single photon detection capability. The breakdown voltage of the APDs is in the range of30V and50～60V at roon temperature, the corresponding dark current at0.95Vb is in the range of0.5nA to lOnA. The Capacitive-Balanced Gate-Pulse method is used to test the capability of single photon detection. When the gate pulse frequency is1.5MHz, the dark counts rates is3.6E-4/ns*pulse, while it is3.5E-4/ns*pulse when the pulse frequency is5MHz for the detection efficiency10%(corresponding gate pulse width:4ns).4. The effects of carrier lifetime on the dark current of APDs are studied theoretically. The results shows that the dark current of SAGCM InGaAs/InP APDs is dominated by the tunneling current in the multiplication layer and thermal generation-recombination (GR) current in the absorption layer, and this thermal GR current only influences the dark current after Vp. We extracted the minority carrier lifetime of the InGaAs absorption layer and InP multiplication layer in our fabricated APDs to be100ns and20ps, respectively. This short carrier lifetime in InGaAs absorption layer causes the thermal GR current in InGaAs layer to be the dominated one in the fabricated APDs, which outcome is that the dark current rises greatly(almost1magnitude, le-10to le-9A) at the punch-through voltage.5. The effects of surface charge on the dark current of the Separate, Absorption, Grading, Charge, Multiplication (SAGCM) InGaAs/InP avalanche photodiodes (APDs) are discussed using drift-diffusion simulation. The surface charge is mainly duo to the injected hot holes from the p+InP layer and the InP surface defects. The dark current increases exponentially with the increasing of surface charge density, and gets multiplied, thus influencing the performance of the APDs, especially in Geiger mode. A surface charge leakage current mode is proposed to illustrate the effects of surface charge, and the Flouting Guard Ring(FGR) structure can suppress effectively the surface charge leakage current. Meanwhile, we have used this model to explain theoretically the negative temperature characteristic in the dark current under low voltage.6. We proposed an APDs structure coupled with a novel metal-insulator-metal (MIM) grating. The dark current of APDs can be reduced by decreasing the size of the APD device under almost the same light quantum efficiency precondition since the light is focused by the MIM grating. This method can achieve a ultimate size of APD(diameter less than5microns). As a previous study, we simulated the light focus properties of the MIM grating, the results shows that the convergence of the light can be up to7times. In addition, we also have done some exploration for the MIM grating fabrication processes.