GB2284708A - Method for passivation of multi-quantum well infrared photodetectors (QWIPS) to reduce dark current and to improve dark current uniformity - Google Patents

Method for passivation of multi-quantum well infrared photodetectors (QWIPS) to reduce dark current and to improve dark current uniformity Download PDF

Info

Publication number
GB2284708A
GB2284708A GB9424181A GB9424181A GB2284708A GB 2284708 A GB2284708 A GB 2284708A GB 9424181 A GB9424181 A GB 9424181A GB 9424181 A GB9424181 A GB 9424181A GB 2284708 A GB2284708 A GB 2284708A
Authority
GB
United Kingdom
Prior art keywords
wafer
quantum well
dark current
passivation
detectors
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9424181A
Other versions
GB9424181D0 (en
Inventor
John Lopata
Lars Christian Luther
Jr John William Stayt
Venkataraman Swaminathan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
AT&T Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by AT&T Corp filed Critical AT&T Corp
Publication of GB9424181D0 publication Critical patent/GB9424181D0/en
Publication of GB2284708A publication Critical patent/GB2284708A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/3003—Hydrogenation or deuterisation, e.g. using atomic hydrogen from a plasma
    • H01L21/3006—Hydrogenation or deuterisation, e.g. using atomic hydrogen from a plasma of AIIIBV compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/1446—Devices controlled by radiation in a repetitive configuration
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • H01L31/035236—Superlattices; Multiple quantum well structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • H01L31/035272—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions characterised by at least one potential jump barrier or surface barrier
    • H01L31/035281—Shape of the body
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1868—Passivation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electromagnetism (AREA)
  • Manufacturing & Machinery (AREA)
  • Nanotechnology (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biophysics (AREA)
  • Optics & Photonics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Plasma & Fusion (AREA)
  • Light Receiving Elements (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Radiation Pyrometers (AREA)
  • Solid State Image Pick-Up Elements (AREA)
  • Formation Of Insulating Films (AREA)
  • Testing Or Measuring Of Semiconductors Or The Like (AREA)

Abstract

A method for passivating multi-quantum well wafers to reduce dark current and to improve dark current uniformity. The method comprises the steps of growing a wafer having a multi-quantum well structure, exposing at least a portion of the wafer to a hydrogen plasma and processing the wafer to form several discrete infrared photodetectors as well as detector arrays. The method finds application in GaAs/AlGaAs multi-quantum well detectors, in particular staring focal plane arrays (FPAs). <IMAGE>

Description

Method for Passivation of Multi-Quantum Well Infrared Photodetectors (QWIPS) to Reduce Dark Current and to Improve Dark Current Uniformity Field of the Invention The invention generally relates to the field of semiconductor processing, and more particularly, to a method for passivation of multi-quantum well infrared.
photodetectors (QWIPS) to reduce a parasitic current, known otherwise as dark current or leakage current and to decrease the non-unifoimity in this current in a product, known as infrared focal plane arrays (FPAs), formed from QWIPS.
Related Art Low noise large area infrared detectors responding in the 8-12 micron as well as 3-5 micron wavelength ranges are of interest for many commercial and military applications for the purpose of infrared (IR) sensing. These detectors are generally deployed in the form of an array, which can be a l-dimensional (l-D) linear array, also known as a scanning array, or can be a 2-dimensional (2-D) array, also known as a 'staring' array. The individual detectors which make up the array are referred to as pixels - The basic principle of infrared detection, which is independent of the configuration of detectors used, namely, 1-D or 2-D arrays, is that an object which needs to be detected and subsequently recognized and identified, must have a difference in temperature from that of the background in which it is located. The ability of the IR detector to distinguish an object in a background based on the temperature differences between them is defined as the sensitivity of the detector. In the IR parlance this sensitivity is referred to as the Noise Equivalent Differential Temperature (NEDT) which, in other words, defines the Signal to Noise (S/N) ratio of the IR detector.
The signal of an IR detector is the photocurrent generated in it by the infrared photons falling on the detector. The photocurrent is read using suitable electronic read-out circuitry such as a Complementary Metal Oxide Semiconductor (CMOS) multiplexer. To achieve high sensitivity, the signal (i.e., the photocurrent) should be significantly higher than the noise which includes statistical fluctuations produced in the current caused by the current generated in the detector by other mechanisms as well as the background current in the read-out circuitry itself. Therefore, for best operation of the detector, or to achieve lowest NEDT, the noise sources should be minimized.
The generation of the photocurrent in the IR detector depends on its design, of which there are of two kinds - photovoltaic and photoconductive. The underlying physics of these two types can be found in Chapter 13 of the book entitled Physics of Semiconductor Devices, S.M. Size, 2nd Ed., Wiley, New York (1981). In a photovoltaic device, the IR radiation produces electron-hole pairs which in turn generate the photocurrent. Contrastingly, in a photoconductive device the IR radiation produces only one type of carrier, either electron or hole, that generates the photocurrent. Apart from this difference, the functionality of the arrays made from either type is the same.
In addition to NEDT (sensitivity), another figure of merit of the IR detector which is related to NEDT is the detectivity of the IR detector, referred to as D (D star) expressed in units of cm (Hertz)1 W-1. It is the S/N ratio when one watt is incident on a detector having a sensitive area of 1 cm2 and the noise is measured with an electrical bandwidth of lHertz. The units of D for convenience are called Jones after the inventor of this quantity. D is also related to the detection range, the range increasing with increasing Ds. D' is usually measured at the specific temperature the IR array is used and is also a function of the voltage bias applied on the detector.
Further description of the IR detector physics can be found in Detection of Optical and Infrared Radiation, by R.H. Kingston, Springer-Verlag, New York (1979).
Of the two types of IR sensor arrays, the staring arrays offer the advantage of increased sensitivity compared to linear arrays, and further, they are mechanically simple in that the scanning elements are not required. Therefore, for large field of view IR imaging systems, staring arrays are very attractive. The sensitivity of a staring array depends very much on the spatial uniformity of the array. Spatial uniformity is interpreted to mean the uniformity in response of the individual pixels which make up the 2-D array. In fact, if the inter-pixel variations are large, the sensitivity can be entirely dorninated by the noise produced by the spatial nonuniformity. It is, therefore, of utmost importance that the non-uniformity of pixel-topixel variations be minimized in a staring array. The non-uniformity can arise for various reasons such as variations in the photocurrent generation, geometry of the pixels and the detector generated dark current. The latter quantity is also known as the leakage current, and is the current produced in the detector due to thermal generation of electrical carriers present at all conditions.
Recently, IR staring arrays have been demonstrated from m-V compound semiconductors, particularly, the GaAs/AlGaAs multi-quantum well infrared photodetectors. (Levine et al., "Long Wavelength 128 x 128 GaAs Quantum Well Infrared Photodetector Arrays," Semicond. Sci. Technol. 6:pC1 14-C119 (1991)). These detectors are referred by the acronym QWIP for Quantum Well Infrared Photodetectors and they are of the photoconductive type. Staring arrays of 128 x 128 pixel size have been successfully made using GaAs/AlGaAs QWIPs. These arrays exhibit a NEDT of 10 milliKelvin (mK) when operated at a temperature of 60-65 Kelvin (K). At this temperature, the array operation is entirely background radiation limited, otherwise known as BLIP operation. At BLIP, the photocurrent exceeds significantly the dark current.
While 10 mK NEDT is very impressive, further advances in QWIP technology is required to achieve the same sensitivity at a higher array operating temperature such as at 77K, a temperature easily obtainable with commercially available closed cycle refrigerators. Further, competitive IR technology offered by the material system Mercury-Cadmium Telluride, operates at 77K. What seriously hampers the operation of QWIPs at 77K is the thermally generated dark or leakage current which exceeds the photocurrent such that the array operation changes from BLIP to detector noise limited regime. Under this condition, for an operating temperature around 77K, NEDT increases by nearly an order of magnitude. As the IR sensor operation approaches the detector noise limited regime, the spatial non-uniformity in the dark current becomes important and excessive variations in the dark current from pixel-to-pixel undermines NEDT. (B. Stokes et al., Quantum Well Focal Plane Array - Feasibility Study, Final Report, submitted to U.S. Army Missile Command by Martin-Marietta Missile Systems, (unclassified) (1991)). Dark current variations of as much as 20% can exist in the GaAs/AlGaAs QWIPs. (Swaminathan et al., "Producibility of GaAs/AlGaAs Quantum Well Infrared Photodetector Arrays - Material and Processing Issues," Proceedings of the 1993 IRIS Specialty Group on Infrared Detectors, MITRE Corporation, Bedford, MA, Aug. 16-20, 1993).
If the uniformity of the dark current is improved in the GaAslAlGaAs QWIP staring arrays, the sensitivity will also commensurately increase at the operating temperatures close to 77K. Thus, what is desired is a method to improve the dark current uniformity to enhance sensitivity and make the QWIP technology highly competitive in the IR sensor industry.
Summarv of the Invention The present invention is directed to a method for passivating multi-quantum well wafers to reduce dark current, and the product formed by that method. The method of the present invention comprises a post-growth passivation step. The method begins with a multi-quantum well (i.e., superlattice) wafer that is grown according to well known methods such as vapor phase epitaxial techniques. According to the present invention, the as-grown wafer is then subjected to a hydrogen plasma passivation. After passivation, the wafer is processed according to a well defined set of processing steps to create a plurality of infrared (IR) photodetector devices. Thus, the passivation step is preformed after growth and before device processing.
In a preferred embodiment, the post-growth passivation technique improves the uniformity and performance of GaAslAlGaAs Multi-Quantum Well Infrared Photodetectors (QWIPs). The passivation step involves exposing the as-grown wafer to a hydrogen plasma at relatively low temperatures (200-250"C) such that atomic hydrogen from the plasma penetrates the entire multi-quantum wells. Atomic hydrogen interacts with impurities and defects that are in the bulk as well as in the interfaces between GaAs/AlGaAs quantum wells. These impurities and defects act as compensating centers thereby reducing the free carrier concentration released from the intentionally added dopants in the quantum well. In an as-grown wafer, the current art of crystal growing being what it is, it is conceivable that the concentrations of impurities and defects are spatially inhomogeneous. This gives rise to dark current variation at the detector operating temperature. In addition, the defects themselves can contribute to dark current.
The post-growth passivation technique of the present invention utilizes readily available equipments and can be easily implemented. Passivated QWIP 2-D arrays will exhibit improved uniformity and hence significant performance improvement.
Further, the technique can render a mediocre wafer into a high performance wafer.
The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.
Brief Description of the Drawx The invention will be better understood if reference is made to the accompanying drawings in which: Figure 1 shows a schematic of a standard GaAslA1GaAs multi-quantum well infrared photodetector (QWIP) structure.
Figure 2 shows a representative, high-level flowchart of the method steps according to the present invention.
Figure 3 shows a plot of responsivity (in units of amps per watts on the Y axis) plotted as a function of bias voltage (in volts on the X axis) for a test wafer, half of which was processed according to the present invention.
Figure 4 shows plots of the full field-of-view dark current (Id) at 77K of detectors of 200 micron x 200 micron size made from both halves of the wafer under test as in Figure 3.
Figure 5 shows a plot of the quantum efficiency (llCp) for both halves of the wafer under test as in Figure 3.
Figure 6 shows a plot of D at 77K in units of Jones as a function of applied bias voltage in units of volts.
In the figures, like reference numbers indicate identical or functionally similar features. Also in the figures, the left-most digit of each reference number corresponds to the figure in which the reference number is first used. No attempt has been made to depict true dimensions and/or proportions.
Detailed Description of the Preferred Embodiments Figure 1 shows a schematic of a standard GaAs/AlGaAs multi-quantum well infrared photodetector (QWIP) structure showing the various epitaxial layers that are grown on a 50mm (millimeter) diameter semi-insulating GaAs substrate having a (100) crystallographic orientation. An array 100 comprises a plurality of detectors (pixels) 102 with grating couplers on top of the pixel 102.
The detectors 102 are formed on a substrate 104 comprising semi-insulating GaAs. On substrate 104 is formed a bottom contact layer 106 comprising a 1.0 pm silicon (Si) doped GaAs (GaAs:Si) having a dopant concentration of (1-3)xl0'8cm~3.
The detectors 102 are formed on top of the bottom contact layer 106. Each detector 102 comprises a plurality (e.g., N-50) of quantum wells 108. The quantum wells 108 (also called a superlattice) comprise alternating layers of nominally 40A (angstroms) thick GaAs:Si having a dopant concentration of (l-2)x1018cm3 and 500A thick AlxGal xAs where x is the fraction of Al and is approximately 0.25.
A bonding buffer layer 110 is formed on the quantum wells 108. The bonding buffer layer 110 comprises a 1.0,us GaAs:Si layer having a dopant concentration of (1-3)x1018cm3. An etch stop layer 112 is formed on the bonding buffer layer 110.
The etch stop layer 110 comprises a 0.02clam AlxGalxAs:Si layer having a dopant concentration of (l-3)x1018cm3, where x is approximately 0.25.
A grating and top contact layer 114 are formed on top of the etch stop layers 112 of the detectors 102. The grating and top contact layer comprise a 0.7 llm GaAs:Si layer having a dopant concentration of (1-3)x1018cm3. Metal contact layers are formed on top of the grating contact layer 114, as shown generally at 115. In addition, a metal contact layer 116 is formed.on the bottom contact layer 106 for electrical contact thereto.
A bias voltage is applied to detectors 102 with metal layers 115 functioning as anodes and metal layer 116 functioning as the cathode, as shown by the "+" and "-" symbols in Figure 1, respectively. This scheme of applying voltage to detectors 102 is designated as positive bias direction. In the reverse configuration, namely, metal layers 115 functioning as cathode and metal layers 116 as anode, is designated as negative bias direction. This definition of positive and negative bias is applicable for Figure 3 to 5.
The preferred embodiment of the present invention will now be discussed in detail. While specific features, configurations and arrangements are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other steps, configurations and arrangements may be used without departing from the spirit and scope of the invention.
Figure 2 shows a flow chart of the general steps for preparing a hydrogen.
passivated wafer in accordance with the present invention.. The method begins with a multi-quantum well wafer that is grown according to a method known as molecular beam epitaxy (MBE), as shown generally as process step 202. The inventors used a Varian Gen II MBE machine for depositing the quantum well and other layers shown in Figure 1. The preferred process for preparing (growing) a GaAs/AlGaAs QWIP wafer is described in B.F. Levine et aL, "High Sensitivity Low Dark Current 10 pm GaAs Quantum Well Infrared Photodetectors," Applied Physics Letters, Vol. 56, p. 851 (1990). The method of passivation and the improvements thereupon should equally apply to QWIP wafers grown by other methods as well. The wafer is then subjected to a hydrogen plasma passivation, as shown at a step 204. After the passivation step 204, the wafer is processed according to a well-defined set of processing steps to create a plurality of infrared photodetector devices, as shown at a step 206. The preferred process for creating the photodetectors is disclosed in L.J. Kozlowski et al., "LWIR 128 x 128 GaAs/AlGaAs Multiple Quantum Well Hybrid Focal Plane Array Assessment and Comparison to HgCdTe," Proceedings of the IRIS Specialty Group on Infrared Detectors, NIST, Boulder, Co, Aug. 13-16, 1991, Vol. I, p. 29). According to the present invention, the passivation step is performed after growth of the wafer and before processing of the wafer to form the photodetectors.
In the preferred embodiment of the invention, the passivation step involves exposing the as-grown wafer to a hydrogen plasma at a temperature between 200 and 250"C. At these temperatures, the time of exposure to the hydrogen plasma must be sufficient to cause atomic hydrogen from the hydrogen plasma to penetrate the entire multi-quantum well structure. In this manner, the atomic hydrogen can interact with impurities and defects that are in the wafer substrate and bottom contact layer as well as the entire multi-quantum well structure. The inventors employed a Planaretch II (manufactured by Technics, Inc., located in San Jose, California) plasma system operating at 2500C, H2 pressure 750 millitorr, 50 watts forward plasma power and 30 kiloHertz frequency. The exposure time was kept one hour. Once again, it should be noted that any other technique of hydrogen plasma generation or other methods of atomic hydrogen production can be substituted for the passivation step to obtain the results claimed in this invention.
Without passivation according to the present invention, impurities and defects typically act as compensating centers thereby reducing the free carrier concentration released from the dopants intentionally added during the growth of the quantum wells.
The spatial distribution of these impurities and defects across the 50 mm diameter wafer can be inhomogeneous. This gives rise to dark current variation at the detector operating temperature. In addition, the defects themselves can contribute to dark current.
During post-passivation processing, the hydrogen exposed QWIP wafer is subjected to a temperature of 400"C that causes the dopant passivation to be nullified.
However, the defect passivation is retained and is thermally stable. As a result, the dark current (also commonly referred to as leakage current) uniformity of hydrogen passivated QWIP is improved by a factor of 2 at the detector operating temperatures.
This improvement also manifests a 34 improvement factor in high temperature D of the devices.
Since GaAs/AlGaAs QWIP is an emerging infrared (IR) technology and has shown tremendous promise for staring array applications, improvement of these devices according to the present invention will make these devices operate at higher (77K) temperatures and hence more attractive for staring array applications. Devices make according to the invention have the potential to be used in many current and emerging commercial markets, because of lower cost and ease of productability of this product compared to other competing technologies.
Figures 3-5 show comparative data results obtained by testing a wafer having several nominally identical 200 micron x 200 micron detectors. Half of the wafer was exposed to a post growth passivation according to the present invention and the other half of the wafer was not.
Figure 3 shows a plot of responsivity (in units of amps per watts on the Y axis) plotted as a function of bias voltage (in volts on the X axis). A first curve 302 shows the responsivity of a typical detector from the half of the wafer which was not exposed to the post-growth passivation. A curve 304 represents a typical detector from the other half of the wafer which was exposed to a post-growth hydrogen plasma according to the present invention. Both curves 302 and 304 show that the responsivity of the detector increases as a function of the bias voltage. As the bias voltage increases in either a positive or negative direction, the responsivity flattens out and achieves what amounts to a saturation. The curves 302 and 304 show a very typical behavior for this class of detector for both the passivated and non-passivated halves of the wafer (see, for example, B.F. Levine et aL, "High Sensitivity Low Dark Current 10 pm GaAs Quantum Well Infrared Photodetectors," Applied Physics Letters, Vol. 56, p. 851 (1990)). As is evident by inspection of curves 302 and 304, the overall responsivity of the detector has been lowered because of the post-growth passivation step. However, as noted above in the Related Art section, a more accurate measure of the efficiency of the photodetector is the device detectivity. Thus, the responsivity alone does not provide sufficient information to form an accurate comparison of the passivated and non-passivated halves of the wafer.
Figure 4 is a plot of the full field-of-view dark current (Id) at 77K for detectors from both halves of the wafer under test. The full field-of-view dark current (1d) is plotted logarithmically on the Y axis in units of amps, and is plotted as a function of bias voltage (in volts on the X axis). As stated previously, the detector size is 200 micron x 200 micron. A curve 402 represents the dark current of a detector from the non-passivated half of the wafer. Curve 404 represents the dark current of the detector from the passivated half of the wafer. Since the Y axis scale of the plot is logarithmic rather than linear, it can be observed that the dark current for the detector from the passivated half has been reduced dramatically in accordance with the present invention.
Figure 5 shows a plot of the quantum efficiency (llCp) which is plotted on the Y axis as a percentage (%) which is also plotted as a function of the bias voltage on the X axis. Curves 502 and 504 are very similar in shape to curves 302 and 304 of Figure 3. This is entirely expected based on the relation between responsivity and quantum efficiency of a photoconductor (Detection of Optical and Infrared Radiation, by R.H. Kingston, Springer-Verlag, New York (1979)). Curves 502 and 504 represent the quantum efficiency of detectors from the non-passivated and passivated halves of - the QWIP wafer, respectively.
Since detector D is a more accurate description for the sensitivity of the IR sensor, we now present the comparison of D of detectors from the non-passivated and passivated halves of the wafer. Figure 6 shows a plot of D* at 77K in units of Jones as a function of applied bias voltage in units of volts. Note that D is a measure of the S/N ratio and is obtained by dividing the product of the responsivity (Figure 3) and the square root of the area of the detector (which is 200 pm for the detectors mentioned in our invention) by the noise current. The latter quantity is related to the detector dark current (Figure 4) as noise being proportional to the square root of dark current (for further details see Detection of Optical and Infrared Radiation, by R.H.
Kingston, Springer-Verlag, New York (1979)). In Figure 6, curves labelled 602 and 604 represent the D for the non-passivated and passivated halves of the wafer. It can be seen that the 77K D' for the detector from the passivated half is 34 times better than that of the detector from the non-passivated half. This improvement in D is a direct result of the significant dark current reduction noted in Figure 4 achieved by the post-growth hydrogen passivation claimed in this invention.
Additional tests were performed by the inventors that show increased uniformity of dark current values for the passivated half of the wafer in comparison to the non-passivated half. Tables 14 summarize these additional test results. Table 5 shows the process variables for Tables 14.
Tables 1 and 2 show QWIP 77K full field-of-view Leakage Current (in units of amps) measurements from 200 micron x 200 micron size detectors taken from both halves of the wafer. Table 1 is a summary of the hydrogen annealed half (post-growth passivation) of three 200 x 200 pm detectors at +/-2 and +/-5 volts supplied as a bias voltage. The mean, sigma and sigma/mean of these three detectors are tabulated.
These numbers represent, respectively, the average, the standard deviation, and the ratio of the mean and standard deviation. The value sigma/mean is an indication of the uniformity of the measured detectors with a low value corresponding to high uniformity. Table 2 lists the mean, sigma and the sigma/mean results from three nonpassivated 200 x 200 pm detectors.
Note, for example, the sigma/mean results for the -5 volt bias voltage tests.
The sigma/mean for the hydrogen passivated detectors is 1.57%, compared to the sigma/mean of 4.26% for the equivalent bias voltage of the non-passivated detectors.
A similar observation can be made for other bias voltages also. These results indicate that the spatial uniformity of dark current for the hydrogen passivated detectors is much higher (i.e., less variance) than the spatial uniformity of the dark current between the detectors which were not hydrogen passivated.
Similarly, Tables 3 and 4 show QWIP 30K high background Leakage Current (in units of amps) measurements taken on both halves of the wafer. Again, a comparison of the sigma/mean for the -5 volt bias voltage examples shows a factor of 2 improvement of dark current uniformity between the samples tested. Improvement in uniformity is also noted for other bias voltages.
The plotted results in Figures 3-6 and tabular results of Tables 14 indicate that the reduction of dark current and increased uniformity in dark current illustrate the improvement of the hydrogen passivation of the present invention over the conventional techniques which do not use hydrogen passivation. A reduction of dark current and increase in spatial uniformity of the detectors processed according to the invention are better suited for background limited operation compared to conventional detectors at high (77K) operating temperatures.
Table 1: QWIP 77 K Full Field-of-View Leakage Current (Amps) for Three 200 Micron x 200 Micron Detectors Bias Voltage -5.00 -2.00 2.00 5.00 Bias Field (Kilo VolUcm) -18.5 -7.4 7.4 18.5 1. 6.69E-07 3.96E-07 1.02E-06 3.34E-06 2. 6.72E-07 3.93E-07 1.O5E-O6 3.58E-06 3. 6.93E-07 4.06E-07 1.10E-06 3.79E-06 mean 6.78E-07 3.98E-07 1.06E-06 357E-06 sigma 1.07E-08 5.56E.09 3.30E-08 1.84E-07 sigmal 1.57% 1.40% 3.12% 5.15% mean Table 2: QWIP 77 K Full Field-of-View Leakage Current (Amps) for Three 200 Micron x 200 Micron Detectors Bias Voltage (V) -5.00 -2.00 2.00 5.00 Bias Field (Kilo Volt/cm) -18.5 -7.4 7.4 18.5 1. 1.82E-05 6.23E-06 1.05E-04 1.29E-03 2. 1.72E-05 5.93E-06 1.000-04 1.20E-03 3. 1.64E-05 5.70E-06 9.51E-05 1.13E-03 mean 1.73E-05 5.95E-06 1.00E-04 1.21E-03 sigma 7.36E-07 2.17E-07 4.04E-06 6.55E-05 sigma/ 4.26% 3.65% 4.04% 5.43% mean Table 3: QWIP 30 K High Background Leakage Current (Amps) for Seven 200 Micron x 200 Micron Detectors Bias Voltage (V) -5.00 -2.00 2.00 5.00 Bias Field (Kilo Volt/cm) -18.5 -7.4 7.4 18.5 1. 2.21E-08 157E-08 1.73E-08 1.88E-08 2. 2.11E-08 1.49E-08 1.80E-08 1.89E-08 3. 2.18E-08 1.54E-08 1.67E-OS 1.84E-08 4. 2.22E-08 1.57E-08 1.67E-08 1.87E-08 5. 2.20E-08 1.58E-08 1.93E-08 2.02E-08 6. 2.32E-08 1.64E-08 1.97E-08 2.06E-08 7. 2.28E-08 1.62E-08 1.90E.08 2.00E-08 mean 222E-08 lS7E-08 1.81E-08 1.94E-08 sigma 6.30E-10 4.59E-10 1.16E-09 8.05E-10 sigma/ 2.84% 2.92% 6.40% 4.15% mean Table 4: QWIP 30 K High Background Leakage Current (Amps) for Six 200 Micron x 200 Micron Detectors Bias Voltage (V) 5.00 -2.00 2.00 5.00 Bias Field (Kilo Volt/cm) -18.5 -7.4 7.4 18.5 1. 5.80E-08 2.08E-08 5.17E-08 4.77E-07 2. 6.42E-08 2.32E-08 5.95E-08 6.45E-07 3. 6.25E-08 2.27E-08 5.65E-08 5.41E-07 4. 6.85E-08 2.43E-08 5.79E-08 6.78E-07 5. 6.76E-08 2.39E-08 6.38E-08 7.23E-07 6. 6.60E-08 2.35E-08 6.38E-08 6.33E-07 mean 6.45E-08 231E-08 5.89E-08 6.16E-07 sigma 3.52E-09 1.13E-09 4.22E-09 8.30E-08 sigma/ 5.45% 4.91% 7.17% 13.48% mean Table 5: Process Variables for Tables 1-4 Mask Set: S-CUBED Experiment: Hydrogen Passi vated and non passivated Number of Quantum Wells: 50 Nominal Quantum Well Doping: l.oOE+18 cm3 Device Temperature: 77,30K Black Body Temperature: 900K Test Area: T2-1, T5s6 Modulation Rate: 371151 Hz Pixel Area: 200 ,us2 Well Size: 40 Barrier Size: 500 The hydrogen passivation of the present invention can be extended to other infrared detectors made from m-v and II-VI compounds, such as InP, GaSb, InAs, GaP, AlAs and alloys thereof and HgTe, CdTe, ZnSe and alloys thereof, as well as other photonic and electronic devices such as quantum well strained layer superlattice detectors, quantum well self electro-optic devices, surface emitting lasers, field effect transistors, bipolar transistors, to name a few examples. In other words, in whatever devices where passivation of unwanted impurities andlor defects is desired, a judicious choice of the passivation conditions consistent with other device processing steps can be easily applied with hydrogen passivation as described in this invention.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the scope of the invention.

Claims (10)

Claims:
1. A method for passivating multi-quantum well wafers to reduce dark current and to improve dark current uniformity, comprising the steps of: growing a wafer having a multi-quantum well structure; and exposing a portion of the wafer to a hydrogen plasma.
2. The method of claim 1, wherein said growing step forms a wafer having a GaAs/AlGaAs multi-quantum well structure.
3. The method of claim 2, wherein said exposing step comprises exposing the wafer to the hydrogen plasma at a temperatures between 200-250"C for an hour.
4. The method of claim 3, wherein atomic hydrogen from the hydrogen plasma penetrates the entire GaAs/AlGaAs multi-quantum well structure.
5. The method of claim 3, further comprising the step of processing the wafer to form discrete infrared photodetectors and photodetector arrays.
6. A multi-quantum well wafer produced by a method comprising the steps of: growing a wafer having a multi-quantum well structure; ahd exposing a portion of the wafer to a hydrogen plasma to passivate the multiquantum well structure to reduce dark current.
7. The product formed by the method of claim 6, wherein said growing step of the method forms a wafer having a GaAs/AlGaAs multi-quantum well structure.
8. The product formed by the method of claim 7, wherein said exposing step of the method comprises exposing the wafer to the hydrogen plasma at a temperatures between 200-250"C.
9. The product formed by the method of claim 8, wherein atomic hydrogen from the hydrogen plasma penetrates the entire GaAs/A1GaAs multi-quantum well structure.
10. The product formed by the method of claim 8, wherein the method further comprising the step of processing the wafer to form discrete infrared photodetectors and infrared detector arrays.
GB9424181A 1993-12-07 1994-11-30 Method for passivation of multi-quantum well infrared photodetectors (QWIPS) to reduce dark current and to improve dark current uniformity Withdrawn GB2284708A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US16346593A 1993-12-07 1993-12-07

Publications (2)

Publication Number Publication Date
GB9424181D0 GB9424181D0 (en) 1995-01-18
GB2284708A true GB2284708A (en) 1995-06-14

Family

ID=22590129

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9424181A Withdrawn GB2284708A (en) 1993-12-07 1994-11-30 Method for passivation of multi-quantum well infrared photodetectors (QWIPS) to reduce dark current and to improve dark current uniformity

Country Status (3)

Country Link
JP (1) JPH07202251A (en)
KR (1) KR950021166A (en)
GB (1) GB2284708A (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0211634A2 (en) * 1985-08-02 1987-02-25 Sel Semiconductor Energy Laboratory Co., Ltd. Method and apparatus for manufacturing semiconductor devices
WO1990002416A1 (en) * 1988-08-18 1990-03-08 Centre National De La Recherche Scientifique (Cnrs) METHOD FOR NEUTRALIZING ACCEPTORS ATOMS IN InP OF p TYPE
JPH1059968A (en) * 1996-06-07 1998-03-03 Hoechst Ag End aminated alkynol side chain-containing xanthin compound

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0211634A2 (en) * 1985-08-02 1987-02-25 Sel Semiconductor Energy Laboratory Co., Ltd. Method and apparatus for manufacturing semiconductor devices
WO1990002416A1 (en) * 1988-08-18 1990-03-08 Centre National De La Recherche Scientifique (Cnrs) METHOD FOR NEUTRALIZING ACCEPTORS ATOMS IN InP OF p TYPE
JPH1059968A (en) * 1996-06-07 1998-03-03 Hoechst Ag End aminated alkynol side chain-containing xanthin compound

Also Published As

Publication number Publication date
JPH07202251A (en) 1995-08-04
KR950021166A (en) 1995-07-26
GB9424181D0 (en) 1995-01-18

Similar Documents

Publication Publication Date Title
Walther et al. Growth of InAs/GaSb short-period superlattices for high-resolution mid-wavelength infrared focal plane array detectors
Rehm et al. InAs/GaSb superlattice focal plane arrays for high-resolution thermal imaging
US6657194B2 (en) Multispectral monolithic infrared focal plane array detectors
Varesi et al. Fabrication of high-performance large-format MWIR focal plane arrays from MBE-grown HgCdTe on 4 ″silicon substrates
Tang et al. High-temperature operation normal incident 256/spl times/256 InAs-GaAs quantum-dot infrared photodetector focal plane array
Walther et al. 256× 256 focal plane array midwavelength infrared camera based on InAs/GaSb short-period superlattices
Rehm et al. Type-II superlattices: the Fraunhofer perspective
Arslan et al. \(640\times 512\) Extended Short Wavelength Infrared In 0.83 Ga 0.17 As Focal Plane Array
Razeghi et al. Recent advances in LWIR Type-II InAs/GaSb superlattice photodetectors and focal plane arrays at the center for quantum devices
Razeghi et al. High-operating temperature MWIR photon detectors based on Type II InAs/GaSb superlattice
Rehm et al. InAs/(GaIn) Sb short-period superlattices for focal plane arrays
Cheng et al. 2.45-μm 1280× 1024 InGaAs focal plane array with 15-μm pitch for extended SWIR imaging
Rhiger et al. Progress with type-II superlattice IR detector arrays
Andersson et al. 320 x 240 pixels quantum well infrared photodetector (QWIP) array for thermal imaging: fabrication and evaluation
Razeghi et al. Recent advances in high-performance antimonide-based superlattice FPAs
Walther et al. Infrared imaging with InAs/GaSb type‐II superlattices
Alchalabi et al. Monolithic heteroepitaxial PbTe-on-Si infrared focal plane array with 96× 128 pixels
US5241196A (en) Photoresponsive device including composition grading and recessed contacts for trapping minority carriers
Krishna et al. Two‐color focal plane arrays based on self assembled quantum dots in a well heterostructure
GB2284708A (en) Method for passivation of multi-quantum well infrared photodetectors (QWIPS) to reduce dark current and to improve dark current uniformity
Rutz et al. InAs/GaSb superlattice focal plane array infrared detectors: manufacturing aspects
Gravrand et al. Status of very long infrared-wave focal plane array development at DEFIR
Rehm et al. InAs/GaSb superlattice focal plane arrays for high-resolution thermal imaging
Johnson et al. Status of HgCdTe/Si technology for large format infrared focal plane arrays
Walther et al. III-V semiconductor quantum well and superlattice detectors

Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)