When the In composition in the InGaAs material reaches 0.53, and Ga reaches 0.47, InGaAs / InP lattice matched makes it can form a heterojunction. The InGaAs / InP heterojunction structure utilizes the steps of the conduction band and valence band formed by the difference in the band gap of the two materials as the potential barrier to limit electrons and holes in the active region, so it is easy to generate light gain. Besides, the refractive index optical waveguide formed by the difference in refractive index between the two materials can effectively confine the optical mode in the active region, thereby reducing internal losses and improving photoelectric conversion efficiency. With years of production experience and expertise, PAM-XIAMEN can offer high quality 2″ InP / InGaAs / InP epitaxial structure as follows:

1. Specification of InGaAs on InP (100) Substrate

InP Substrate:

Indium Phosphide wafers,

P/E 2″dia×350+/-25um,

n-type InP:S

(100)+/-0.5°,

EDP<1E4/cm2.

One-side-polished, back-side matte etched, SEMI Flats.

EPI layer:

Epi 1: InGaAs:(100)

       Thickness:100nm,

       etching stop layer

Epi 2: InP:(100)

       Thickness:50nm,

        bonding layer

2. About InGaAs / InP Growth

The InGaAs / InP PIN detector is fabricated by growing the lattice-matched In0.53Ga0.47As on the n-type InP substrate and then growing InP as the capping layer. Please remark to make a 2.6um photodetector, a composition gradient layer whose composition varies linearly with thickness (x is gradient from 0.53 to 0.81) after the growth of the lattice-matched InGaAs epilayer.

The InP bonding layer is also an ohmic contact layer. Heavy doping is to facilitate the formation of ohmic contact with the electrodes. The forbidden band width of InP is larger than that of In0.53Ga0.47As, so the bonding layer is also a cap layer, which can reduce the influence of reverse dark current.

The InGaAs / InP photodiode fabricated with heterojunction structure has following characteristics:

There is an existence of a unique window effect;

The frequency characteristics depend on the relative absorption of the incident light in the two materials of the heterojunction. The incident light is projected on the InP side of the heterojunction with a wider band gap, and the incident photons can smoothly pass through the InP, then enter the InGaAs to be absorbed;

The absorption wavelength range of the photodetector with InGaAs / InP double heterojunction structure is 0.93um~1.7um.

3. Comparison for PIN Photodetectors with Single and Double Heterojunctions

Heterojunction PIN photodetectors can be divided into single heterojunction photodetectors (SHPD) and double heterojunction photodetectors (DHPD), which differ in quantum efficiency, frequency response and dark current.

For single heterojunction photodetectors, take the InGaAs / InP heteroepitaxial structure: p-InGaAs / i-InGaAs/ n-InP substrate for example. When the photosensitive surface radius of SHPD is 10um and the ratio of P region thickness to electron diffusion length is less than 0.2, the quantum efficiency decreases by less than 0.32%, and the bandwidth increases by about 0~4%. For the dark current determined by the bulk effect, SHPD Slightly better. So it can conclude that when the photosensitive area is small and the thickness of the P region is thin, the performance of SHPD and DHPD with are comparable, which provides a basis for the design of high-speed optical detectors for high-performance broadband optical networks.

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