The influence of various profile distributions of AIIIBV grading layers composition and layers configuration on the photo-detector spectral characteristics are discussed.
With the decreasing of doping concentration, the electric field between the absorption layer and the grading layer increases, which makes the electron more easier to punch through the absorption layer and the grading layers, so the punchthrough voltage decreases, owing to the wedge-shaped electric field profile with a high gradient [12].
The Grading layer (Sub-G) was composed of CdxZn1−xO with a gradual decrease of x across the profile, changing from 0.2 to 0.55, aiming to photon absorption from 2.0 to 3.0 eV.
By comparing different profile types (normal profile, reverse profile and no profile), the normal profile was formed in sequence by the superposition of a high Ge content layer, a Ge content grading layer and a μc-Si H layer has been proposed.
The structures from top to bottom are sequentially named as InGaAs contact layer, InAlAs cladding layer, InAlGaAs grading layer, InGaAs absorption layer, InAlGaAs grading layer, InAlAs charge layer, InAlAs multiplication layer, InAlAs cladding layer, InP contact layer, and InP substrate.
It is a simplified SACM APD structure that ignores grading layer.
From the top to the bottom, these layers are sequentially named as contact layer, window layer, absorption layer, grading layer, charge layer, multiplication layer, InAlAs buffer layer, InP buffer layer, and InP substrate.
From the electric field distribution, with the increasing thickness of multiplication layer, the electric field in the absorption layer and the grading layer decreases, making the electrons more difficult to punch through the layers, so the punchthrough voltage increases.
With the increasing thickness and the doping of charge layer, the electric field in the absorption layer and the grading layer decreases, and it makes the electron more difficult to punch through the layers, so the punchthrough voltage increases, but the electric field in multiplication layer increases with the increased thickness and the doping of charge layer.
From the FEM analyses, the optimal gradient structure design was obtained corresponding to the following parameters: the number of graded layers n = 2 and the thickness of graded structure t = 1 mm.
The laminated plate is composed of perfectly bonded CNT-reinforced functionally graded layers.
