Abstract
This letter reports on a lateral linear mode avalanche photodiode through 0.35 μm high voltage CMOS process. The linear mode avalanche photodiode is designed and fabricated with the lateral separate absorption, charge and multiplication (SACM) structure using an epitaxial wafer. The DNTUB layer, DPTUB layer, Pi layer and SPTUB layer are used for the lateral SACM structure. This improves freedom of the design and fabrication for monolithic integrated avalanche photodiode without high voltage CMOS process modifications. The breakdown voltage for the lateral linear mode avalanche photodiode is about 114.7 V. The dark currents at gain M = 10 and M = 50 are about 15 nA and 66 nA, respectively. The effective responsive wavelength range is 450 ~ 1050 nm. And the peak responsive wavelength is about 775 nm at 20 V while M = 1. With unity gain (M = 1), the responsivity at 532 nm is about half of the maximum.
Optical detection of visible and near-infrared (NIR) radiation (λ < 1100 nm) has been focused on various developments of silicon avalanche photodiodes (APDs). APD is a semiconductor photodetector in which a photon carrier can be generated due to photoelectric effect of solid-state semiconductor materia
However, with the limitations of design rules for most CMOS process, it is extremely difficult to achieve a suitable charge layer which is used to modulate the electric field in multiplication region for the vertical SACM APDs. Until now, most commercial SACM APDs have not been able to meet the requirements of low-cost, high-performance, monolithic integration and large-scale arrays. And only units APD or small-scale linear array APD can be fabricated and available. In order to design and fabricate vertical SACM APD through CMOS process without any process modification there are two design approaches which are usually carried out to get a suitable charge layer. The first way is the transverse space doping modulation. The groups have designed several silicon APDs by applying lateral well modulatio
In this letter, we report the fabrication and characterization of lateral linear mode avalanche photodiode based on 0.35 μm high voltage CMOS process without any technology rules modification. This linear mode APD is fabricated with the lateral SACM structure using the 15 μm thick epitaxial layer. The photosensitive surface is an octagonal regio
The cutaway schematic (not to scale) of the lateral SACM APD presented in this paper is seen from

Fig. 1 Schematic views of APD (a) cross section, (b) simplified electric field distribution, (c) the microscopic picture of the complete APD device, (d) the microscopic picture of the photosensitive region (Unit: μm)
图1 APD示意图(a)横截面,(b)电场分布,(c)APD器件的显微照片,(d)光敏区的显微照片(单位:μm)
The light current and dark current of the lateral APD are measured through Keithley 4200A-SCS Parameter Analyzer. The unity gain for M = 1 is defined at the low reverse bias voltage of 20 V. Furthermore, the breakdown voltage of the lateral APD is defined as the reverse voltages at which the dark current reaches 1 μ

Fig. 2 Currents vs. reverse bias voltage
图2 电流-反向偏置电压特性
The photocurrent multiplication gain defined through
, | (1) |

Fig. 3 Multiplication gain vs. reverse bias voltage
图3 增益-反向偏置电压特性
The normalized spectral responsivity for the lateral linear mode APD is obtained at the low bias voltage of 20 V with unity gain (M = 1) with the spectral responsivity test system and is shown in

Fig. 4 Normalized responsivity vs. wavelength (450 ~ 1050 nm)
图4 归一化响应-波长特性
The lateral linear mode avalanche photodiode with the photo sensitive area of 618 μ
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