Method of fabricating a surface coupled InGaAs photodetector

Details Method of fabricating a surface coupled InGaAs photodetector Method of fabricating a surface coupled InGaAs photodetector

1999-05-13

2001-05-08

Mulpuri, Savitri (Department: 2812)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S605000, C438S745000

Reexamination Certificate

active

06228673

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the fabrication of photodetectors, and, more particularly, to the fabrication of an InGaAs PIN photodetector having high optical-power handling capability with good linearity of conversion to an electrical signal.
A photodetector is a device that converts incident light into an electrical signal. A light beam is directed onto the photodetector, and the electrical output signal of the photodetector is a measure of the incident energy of the light beam. Photodetectors are available for both visible and infrared light energy.
Photodetectors are used in a wide variety of applications. For some, the photodetector need only detect the presence of light, and its other component capabilities are not important.
In other applications, however, the photodetector is used in a signal processing or handling system. The photodetector may act as a part of a signal handling system to convert incident light to an electrical signal for transmission or processing. The photodetector must therefore be capable of handling the desired input power of the light beam, and achieving the conversion to an electrical signal with good linearity, good frequency range, and low distortion.
A well known photodetector for the near infrared light range is the InGaAs PIN diode. In one version, this diode has a p+ doped InGaAs layer and an n+ InP layer, on either side of an undoped InGaAs layer, with this structure supported on a light-transparent InP substrate. Light incident on the front side of the substrate produces a voltage between the p+ doped InGaAs layer and the n+ InP layer, which voltage is generally proportional to the intensity of the incident light.
While operable, this InGaAs PIN diode has some shortcomings for particular applications, such as CATV analog transmission systems using RF and microwave antenna networks. For such systems to achieve their best performance, the maximum light intensity must be in the range of greater than 10 milliwatts (mW) of optical signal strength and the light-to-electrical signal conversion must have good linearity. Semiconductor lasers capable of producing an optical signal output in the range of a few tens of milliwatts are now available. However, most existing InGaAs PIN photodiodes are limited to about 2 mW of incident optical signal strength. The systems using the available InGaAs PIN photodiodes therefore cannot take advantage of the capabilities of the higher-power semiconductor lasers. Accordingly, the available photodetectors limit the performance of these systems.
There is a need for an improved photodetector which can handle high incident optical intensities and convert them to electrical signals with good linearity. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a fabrication technique for InGaAs PIN diodes. The diodes of the invention are operable to light intensities of greater than 15 mW, with good linearity of conversion to an electrical signal and low noise. The diode is operable over a broad frequency range extending into microwave frequencies. The InGaAs PIN diode of the invention utilizes a known basic structure, with the fabrication processing optimized for good performance.
In accordance with the invention, a method for fabricating a photodetector, utilizes a multilayer structure comprising a semi-insulating InP substrate, an n+ InP contact layer overlying the InP substrate, an undoped InGaAs absorbing layer overlying the n+ InP contact layer, and a p+ doped InGaAs layer overlying the undoped InGaAs absorbing layer. The method of the invention includes depositing a passive metal p-contact dot onto the p+ doped InGaAs layer of the multilayer structure, and etching a mesa structure into the multilayer structure. The mesa structure includes the passive metal p-contact dot, the p+ doped InGaAs layer, and the undoped InGaAs absorbing layer. The step of etching is performed with an etchant that does not attack the n+ InP contact layer and the InP substrate. The method further includes patterning the n+ InP contact layer, depositing a passive metallic n-contact layer onto the patterned n+ InP contact layer, and depositing a patterned organic polymer insulator layer overlying a portion of the structure. The patterned organic polymer insulator layer does not cover the passive metal p-contact dot and the metallic n-contact layer. The patterned organic polymer insulator layer is thereafter cured, and the device is passivated. Metallic contact traces are deposited, with a first trace extending to the passive metal p-contact dot and a second trace extending to the metallic n-contact layer.
The preferred multilayer structure includes the approximately 1 micrometer thick InP contact layer that is doped n+ with silicon or tin to a concentration of about 1×10
19
atoms per cubic centimeter. The absorbing layer is “undoped” InGaAs, where the term “undoped” indicates an absence of intentional doping and a background concentration of less than about 5×10
15
atoms per cubic centimeter. The doped InGaAs layer is doped p+ with beryllium or zinc to a concentration of about 1×10
19
atoms per cubic centimeter.
The passive metal p-contact dot is preferably gold-beryllium metal. The metallic n-contact layer is preferably formed of multiple sublayers, including a gold-germanium layer, a nickel layer, and a gold layer. The organic polymer insulator is preferably a polyimide, which is cured and passivated by heating in a nitrogen atmosphere. The metallic contact traces are preferably thick gold layers, most preferably from about 2.5 to about 3 micrometers in thickness.
The mesa structure is etched with an etchant that attacks the InGaAs layers, but not the InP layers. The preferred etchant is based on citric acid, most preferably an aqueous solution of citric acid, hydrogen peroxide, and phosphoric acid.
Prototypes of the InGaAs PIN photodiode of the invention have been measured to reproducibly produce a highly linear output over a range of light intensities from zero to over 15 mW, and in some cases to as high as 20 mW. The photodiode is operable over a wide bandwidth from dc to 20 GHz. Other performance features of the photodiode are also excellent.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.


REFERENCES:
patent: 4441187 (1984-04-01), Bouley et al.
patent: 4996163 (1991-02-01), Sasaki
patent: 5250471 (1993-10-01), Kogure et al.
patent: 5266518 (1993-11-01), Binsma et al.
patent: 5444274 (1995-08-01), Sasaki
patent: 5448099 (1995-09-01), Yano
patent: 5475256 (1995-12-01), Sawada et al.
patent: 5518934 (1996-05-01), Forrest et al.
patent: 5552629 (1996-09-01), Watanbe et al.
patent: 5646069 (1997-07-01), Jelloian et al.
patent: 5684308 (1997-11-01), Lovejoy et al.
patent: 5689122 (1997-11-01), Chandrasekhar
patent: 5966622 (1999-10-01), Levine et al.
patent: 6005266 (1999-12-01), Forrest et al.

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