Abstract:
Pixels in a focal plane array are defined by controlled variation of the Fermi energy at the surface of the detector array. Varying the chemical composition of the semiconductor at the detector surface produces a corresponding variation in the surface Fermi energy which produces a corresponding variation in the electric field and electrostatic potential in the bulk semiconductor below the surface. This defines pixels by having one Fermi energy at the surface of each pixel and a different Fermi energy at the surface between pixels. Fermi energy modulation can also be controlled by applying an electrostatic potential voltage V1 to the metal pad defining each pixel, and applying a different electrostatic potential voltage V2 to an interconnected metal grid covering the gaps between all the pixel metal pads. Methods obviate the need to etch deep trenches between pixels, resulting in a more manufacturable quasi-planar process without sacrificing performance.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/748,958, filed Jan. 4, 2013. This application is herein incorporated in its entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to focal plane array (FPA) sensors, and more particularly, to a focal plane array with pixels defined by modulation of surface Fermi energy. 
     BACKGROUND OF THE INVENTION 
     Focal plane arrays typically consist of two dimensional arrays of individual and separate detectors—or pixels—which must be physically isolated from one another (mesas) in order to be able to generate an image of a scene devoid of any crosstalk or signal admixture between adjacent pixels. The detectors themselves are commonly made of an appropriate semiconductor material, regions of which can be doped either p-type or n-type. The junction between regions of opposite doping characters forms a so-called p-n photodiode which has the important ability to generate an electrical current when exposed to the appropriate illumination. While the doping can be created in a two dimensional pattern of islands in bulk material by techniques such as impurity diffusion or ion implantation, modern focal plane arrays are commonly fabricated by methods such as molecular beam epitaxy (MBE) or chemical vapor deposition (CVD). In MBE and CVD, semiconductor layers of different doping types are epitaxially grown sequentially in situ. In this case, the p-n junction is buried at some depth below the surface of the wafer down the sequence of grown layers over the entire substrate. Subsequent processing demands that trenches be etched in a two-dimensional mesa pattern in order to define individual pixels. Indeed, vertical mesa walls can be several microns deep. There are significant drawbacks to the requirement that trenches be etched in a two-dimensional mesa pattern in order to define individual pixels. First, the fabrication becomes significantly more complicated. Second, the etching exposes the p-n junction, introducing the possibility of surface leakage current, which often requires some passivation technique to mitigate. U.S. patents describing photodetector design approaches include U.S. Pat. Nos. 7,687,871, 7,737,411, 7,795,640, 7,928,473, 8,003,434, 8,004,012, and U.S. Pat. No. 8,274,096. Papers describing effects include Chanh Nguyen, Berinder Brar, Herbert Kroemer, and John H, English, Surface donor contribution to electron sheet concentrations in not intentionally doped InAsAlSb quantum wells, Applied Physics Letters, vol. 60, No. 15, 13 Apr. 1992, pages 1854-1856 and Chanh Nguyen, Berinder Brar, Vijay Jayaraman, Axel Lorke, and Herbert Kroemer, Magnetotransport in lateral periodic potentials formed by surface layer induced modulation in InAsAlSb quantum wells, vol. 63, No. 16, 10 Oct. 1993, pages 2251-2253. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     What is needed is a focal plane array that is simpler to fabricate and that mitigates surface current leakage without passivation. 
     SUMMARY OF THE INVENTION 
     Embodiments address these needs with a focal plane array (FPA) where the pixels are defined, not by the usual methods of selective diffusion or selective ion-implantation or etching trenches (i.e. removing detector material between pixels), but by a deliberate and controlled variation of the Fermi energy at the surface of the detector array. Embodiments dispense entirely with any deep etching to delineate individual pixels. They rely, instead, on very shallow etching of a single cap layer that is typically no more than 200 Angströms thick. The p-n junction proper remains safely buried well below the surface of the semiconductor material, thereby minimizing the possibility of detrimental surface leakage. The absence of vertical mesa walls—potentially several microns deep—affords a much simplified fabrication process resulting in a quasi planar structure during detector fabrication. 
     The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter. The invention is susceptible of many embodiments. What follows is illustrative, but not exhaustive, of the scope of the invention. 
     One embodiment provides a semiconductor planar structure device comprising at least one region defined by controlled variation of the Fermi energy at a surface comprising at least one pixel comprising a pixel pad having a perimeter; a gap surrounding the perimeter of the pixel pad; a detector layer beneath the at least one pixel pad and the gap, wherein the pixels are defined by having a first Fermi energy at a surface of each the pixel pad and a second Fermi energy at a surface at the gap between the pixels, whereby variation between the first Fermi energy and the second Fermi energy produces a corresponding lateral variation in the electric field and the electrostatic potential in the detector layer below the surface of the pixel pad and the gap. In another embodiment, the device is a high operating temperature midwave infrared focal plane array with a half maximum cutoff wavelength of about 5.1 microns. For a further embodiment, the detector layer comprises a bulk semiconductor whose energy bandgap, and therefore cutoff wavelength, is determined by material composition of the bulk semiconductor, with a cutoff wavelength between about 400 nanometers (ultraviolet) and about 1 millimeter (far infrared). In a subsequent embodiment, the detector layer comprises a superlattice whose energy bandgap, and therefore cutoff wavelength, is determined by the materials and the period of the superlattice, with a cutoff wavelength between about 400 nanometers and about 1 millimeter. Other embodiments further comprise a readout multiplexer to generate video imagery. For following embodiments, the device comprises a type II superlattice wherein high contrast images are produced by the detector device when used in an imaging system. Yet other embodiments provide that the Fermi energy variation is controlled by applying an electrostatic potential voltage V 1  to a metal pad defining each pixel and applying a different electrostatic potential voltage V 2  to an interconnected metal grid within the gaps between the metal pads defining each pixel. For other embodiments, the detector layer comprises sequentially deposited semiconductor planar layers forming either a p-n junction or an n-p junction configured to generate a photocurrent when illuminated by light radiation; a planar semiconductor first cap layer above the detector, the first cap layer comprising a first semiconductor material; a planar semiconductor second cap layer above the first cap layer, the second cap layer comprising a second semiconductor material, the gap being defined by selectively removing the second cap layer in the region between pixels, wherein the first semiconductor material and the said second semiconductor material are dissimilar; the first semiconductor material and the second semiconductor material having different surface state characteristics such that the Fermi level at the surface of the first cap layer is pinned at a first Fermi energy level and the Fermi level at the surface of the second cap layer is pinned at a second Fermi energy level, and wherein the first Fermi energy level is not equal to the second Fermi energy level. In additional embodiments, an optically active part of the detector comprises one or more barriers, wherein the one or more barriers curtail the magnitude of generation-recombination currents within junction regions, whereby performance does not degrade at higher temperature operations compared to p-n or n-p junction photodiodes that exclude the one or more barriers. In some embodiments, contact to each pixel is through a metal contact pad deposited on top of each of the second cap layer pixel pads. Additional embodiments provide that surface leakage currents are eliminated because edges of the p-n or n-p junctions are buried in an interior of the semiconductor structure, not exposed to a semiconductor surface. For embodiments, the optical fill factor is 100%. In alternate embodiments, lateral conductivity of the first cap layer in the gaps between the pixels is reduced so that inter-pixel crosstalk is about zero. In included embodiments the thickness of the first cap layer is about 200 Angströms, the thickness of the second cap layer is about 200 Angströms, and the depth of the gap between pixels is about 200 Angströms. In alternate embodiments, the second cap layer is etched away producing the pixel pads so as to leave only the first cap layer in a two dimensional array of semiconductor islands in such a way that the transfer of surface charge carriers leads to one carrier density in the interior of the islands and another, different, carrier density in the interior of regions between the islands, resulting in a two dimensional modulation of carrier concentration. In embodiment examples, etching of the second cap layer exclusively defines a two dimensional array of individual pixels, excluding etching deep trenches for p-n or n-p junctions. 
     One more embodiment provides a method for fabricating a focal plane array (FPA) comprising providing a substrate; providing a common contact layer on the substrate; providing an absorber layer on the common contact layer; providing a barrier layer on the absorber layer; providing a cap one layer on the barrier layer; providing a cap two layer on the cap one layer; selectively etching the cap two layer to delineate pixels of the FPA; providing a metal contact layer on the defined cap two layer; and providing a metal common contact layer to the common contact layer. In a plurality of embodiments, the barrier layer comprises aluminum arsenide antimonide (AlAsSb); the absorber layer comprises a Type II superlattice; the cap one layer comprises gallium antimonide (GaSb), and the cap two layer comprises indium arsenide (InAs). 
     A further embodiment provides a high operating temperature midwave infrared focal plane array detector system comprising a substrate layer comprising gallium antimonide (GaSb); a common conducting layer on the substrate; an absorber layer comprising a Type II superlattice; a barrier layer on the absorber layer, thickness of the barrier layer being between about 0.1 micron and about 0.5 micron, doping of the barrier layer being less than about 1e16 cm −3 ; a first cap layer comprising gallium antimonide (GaSb), thickness of the first cap layer being about 200 Angströms; a second cap layer comprising indium arsenide (InAs), the second cap layer etched to form gaps between pixels of the detector, thickness of the second cap layer being about 200 Angströms, depth of the gaps being about 200 Angströms; at least one metal contact pixel pad, photolithographically formed on top of each pixel, wherein the surface Fermi energy amplitude is about 250 meV, wherein the optical fill-factor is about 100%, wherein the spectrally averaged quantum efficiency is about 85% over a temperature range from about 80K to about 150K, wherein the noise-equivalent temperature difference does not exceed about 30 millikelvin up to an operating temperature of about 130 K with F/4 optics, and a half maximum cutoff wavelength of about 5.1 microns. For following embodiments, each pixel of the detector array is electrically connected to a corresponding unit cell on a matching readout multiplexer array to form a hybrid focal plane array. In at least one embodiment, electrical connections comprise metallic bumps using a metal selected from the group consisting of indium, gold, tin, or a gold-tin alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the overall FPA structure near one edge of the FPA configured in accordance with one embodiment of the present invention. 
         FIG. 2  is a cross-section view of a portion of the FPA structure of  FIG. 1  configured in accordance with one embodiment of the present invention. 
         FIG. 3  is an energy band diagram for cross section A-A′ of  FIG. 2  going vertically through the middle of a pixel from the top surface down to the substrate configured in accordance with one embodiment of the present invention. 
         FIG. 4  is an energy band diagram for cross section B-B′ of  FIG. 2  in the gap between adjacent pixels going vertically from the top surface down to the substrate configured in accordance with one embodiment of the present invention. 
         FIG. 5  is a perspective view of another embodiment of the FPA structure configured in accordance with one embodiment of the present invention. 
         FIG. 6  shows the spectral response of a High Operating Temperature (HOT) midwave material for a pixel delineation technique configured in accordance with one embodiment of the present invention. 
         FIG. 7  shows the noise equivalent temperature difference (NETD) of a HOT midwave focal plane array as a function of device operating temperature configured in accordance with one embodiment of the present invention. 
         FIG. 8  is a plot of the spectrally averaged FPA quantum efficiency plotted against device operating temperature configured in accordance with one embodiment of the present invention. 
         FIG. 9  presents a sequence of frames captured from a focal plane array of temperatures of 80 K up to 170 K configured in accordance with one embodiment of the present invention. 
         FIG. 10  is a flow chart of an FPA fabrication method configured in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments comprise a method of surface Fermi energy modulation by a controlled variation of the chemical composition of the detector surface. The Fermi energy level at which the free surface of a semiconductor is pinned with respect to its energy bandgap is unique to that semiconductor and varies from one semiconductor to another; it is a function of surface states which, in turn, depend on the density and composition of surface oxides as well as surface dangling bonds. The net result is the presence at the surface and some distance below it of a net excess of charge carriers (electrons or holes) or a net depletion of them. 
     Varying the chemical composition of the semiconductor at a detector surface produces a corresponding variation in the surface Fermi energy (e.g. 250 meV in amplitude) which, in turn, produces a corresponding variation in the electric field and electrostatic potential in the bulk semiconductor below the surface. Embodiments exploit this effect to define pixels by having one Fermi energy at the surface of each pixel and a different Fermi energy at the surface between pixels (gaps). The lateral (xy plane) variation in surface Fermi energy translates to a lateral variation in electrostatic potential energy below the surface that matches the surface spatial pattern and whose amplitude decreases with depth, vanishing at large enough depths (typically a few microns). 
     Embodiments use this lateral electrostatic potential modulation to confine charge carriers (both photo and dark) to the area under the pixels and restrict them from neighboring pixels. Photocurrent from each pixel is collected between a single metal contact on the top side of each unit cell and a second electrical contact at the bottom side of all pixels connected in common. 
     Other embodiments include a method of surface Fermi energy modulation comprising applying an electrostatic potential voltage V 1  the metal pad that defines each pixel and applying a different electrostatic potential voltage V 2  to an interconnected metal grid that covers the gaps between all the pixel metal pads. This method is specifically analogous to the first method, except that the surface Fermi energy is now controlled, not by chemistry, but by externally applied voltages. 
     Particular embodiments comprise a strained layer superlattice (SLS) designed to operate in the MidWave InfraRed (MWIR) portion of the electromagnetic spectrum at operating temperatures as high as 150 K (the field is referred to by those skilled in the art as “High Operating Temperature,” or “HOT,” midwave). In the present embodiment, the growth of the absorbing SLS region of the structure is terminated by two successive cap layers. The first cap layer is a layer of gallium antimonide (GaSb), itself covered by a final cap layer of indium arsenide (InAs). Spatial modulation of the pinning position of the Fermi level at the outer surface of the sample is accomplished very simply by etching away the thin InAs layer between pixels. In significant distinction from the prior art, in known systems the photocarriers are transported only in one of the two bands, viz. the valence band. In the present invention, the photocarriers move from one band to the other at the junction between the two cap layers, viz. from valence band to conduction band in the embodiment shown. This is a critical difference that improves the transport and collection of photocarriers in the present invention, compared to the single-band transport in reference patents and papers. Neither cap layer is intentionally doped and, furthermore, both are thin enough—only on the order of a few hundred Angströms each—to not impede current flow in the vertical direction, i.e., across layers to the metal contact. Furthermore, and equally importantly, their lateral conductivity is small enough to effectively prevent any migration of carriers from one pixel to any of the adjacent ones. This is an important attribute to ensure that the FPA will produce sharp, crisp images free of any inter-pixel crosstalk. A further advantage of this design is that given the lack of deeply etched trenches to delineate isolated pixels, excess carriers photo-generated exactly at the mid-point between two adjacent pixels have an equal chance to be swept horizontally to one side or the other and will ultimately be collected by one electrical contact. Since “dead zones” between pixels have been entirely dispensed with, the fill factor is as high as it can be, namely, 100%. 
       FIG. 1  depicts a perspective view  100  of the overall FPA structure near one edge of the FPA. The z-axis, here  135 , is common to each of  FIGS. 1-4 . Structure elements comprise cap one  105 , cap two  110 , gaps  115  between caps, pixel boundaries  120  aligned with the centers of gaps  115 , metal contact pixel pad  125 , common metal contact pad  130 ; proceeding down along z-axis  135  from cap layer one  105  are barrier  140 , absorber  145 , common contact layer  150 , and substrate  155 . Barrier layer  140  and absorber  145  comprise the detector layer(s). 
       FIG. 2  depicts features of the structure of the focal plane array of  FIG. 1  through a cross-section  200 . The z-axis, here  235 , is common to each of  FIGS. 1-4 . A series of semiconductor layers is grown sequentially on a suitable substrate  255 . In embodiments, substrate  255  comprises gallium antimonide (GaSb). The structure includes absorbing/detector region  245 . In embodiments, absorbing region  245  is a generic absorbing region. As in  FIG. 1 , barrier layer  240  and absorber  245  comprise the detector layer(s). For embodiments, “detector” material  245  is a generic photovoltaic diode with the rectifying diode junction close enough to the surface layers as to be affected by the surface Fermi energy modulation. For embodiments, this is approximately less than half a micron from the surface. Modifying the lateral electrostatic potential at the diode junction is important to the physical definition of the pixels. In this embodiment, detector absorber  245  comprises a Type II superlattice designed to have a cutoff wavelength around  5 . 1  microns. Absorbing region  245  is flanked on the bottom side by conducting layer  250  that is common to all pixels. The top side of the detector/absorbing region is comprised of two thin successive cap layers: cap one  205  and cap two  210 . In the present embodiment, first cap layer  205  comprises gallium antimonide (GaSb), while second cap layer  210  comprises indium arsenide (InAs). As shown in  FIGS. 1 and 2 , final InAs cap layer (cap two  210 ) is etched away between adjacent pixels forming gaps  215 . Pixels are defined beneath those areas where the cap layer  210  remains unetched. In embodiments, for the purpose of electrically accessing each pixel, metal contact pixel pads  225  are photolithographically made on top of each pixel. Electrical contact to the other side of the pixels is provided by another, common, metal pad (corresponding to  130  in  FIG. 1 ; not shown in  FIG. 2 , but implied) reaching down to common contact layer  250 . Corresponding to the array described above is readout multiplexer  260  to generate video imagery. Each pixel of the detector array (corresponding to metal contact pixel pads  225 ) is electrically connected to a corresponding unit cell  265  (shown simplified) on matching readout multiplexer array  260  to form a hybrid focal plane array. 
       FIG. 3  shows the band diagram  300  corresponding to a cross section cutting through the middle of a pixel (section A-A′ in  FIG. 2 ). The z-axis, here  335 , is common to each of  FIGS. 1-4 . The figure displays both conduction band E C    365  in region  380  and valence band E v    370 . The detector consists of two parts: (1) a thick “absorber” layer  345  on a more heavily doped contact layer  350  of similar composition as that of “absorber” layer  345 , and (2) a thinner “barrier” layer  340  that resides between absorber  345  and the two cap layers, cap one  305  and cap two  310 . For embodiments, absorber  345  can be made from a variety of semiconductors such as GaAs, AlAs, GaSb, AlSb, InAs, InSb, HgTe, CdTe, etc. or their alloys with the cutoff wavelength defined by the semiconductor&#39;s energy bandgap. For embodiments, the detector&#39;s thickness is typically a few microns (e.g. 4-5 microns) in order to maximize light absorption and detector quantum efficiency and it is typically low-doped (e.g. &lt;1e16 cm −3 ) in order to maximize minority carrier lifetime and therefore minority photocarrier collection at the junction and quantum efficiency. Following absorber layer  345  is barrier layer  340 . For other embodiments, including modeling, the detector&#39;s thickness is less than 1 micron. The barrier is typically thin (e.g. 0.1-0.5 micron) in order to keep the junction as close to the surface as possible, low-doped (e.g. &lt;1e16 cm −3 ) so as to minimize the screening effect by any carriers of the surface Fermi energy on the junction below, and bandgap-engineered in such a way as to not impede the flow of minority photocarriers vertically up from the junction to the cap. The barrier material is typically a semiconductor with an energy bandgap identical to or larger than the absorber and a band-lineup such that the minority photocarriers (holes in the present embodiment) see a negligible potential barrier travelling from absorber to barrier. In embodiments, barrier  340  is aluminum arsenide antimonide (AlAsSb) containing just enough arsenic to minimize lattice mismatch (e.g. 5%-10%). Completing the structure going out toward the surface is GaSb cap layer one  305  followed by InAs cap layer two  310 . The barrier presents an insurmountable obstacle to the flow of majority carriers (electrons in the present embodiment). The minority carriers (holes in the present embodiment), on the other hand, can flow without hindrance from absorber to cap one. The possibility of holes getting trapped in the GaSb cap (keeping in mind that hole wells are inverted upside down along the energy axis when compared to electron wells) is precluded by the very thin dimension of that layer. At the interface between the cap one  305  and cap two  310  layers, the holes get converted into electrons, moving from the valence band of cap one layer  305  into the conduction band of cap two layer  310 . 
       FIG. 4  shows a band diagram  400  similar to the band diagram of  FIG. 3 , but in the gap region between adjacent pixels (section B-B′ in  FIG. 2 ). The z-axis, here  435 , is common to each of  FIGS. 1-4 . The topmost InAs cap layer two ( 210  in  FIG. 2 ) is now absent to reflect the fact that that layer is etched away in that region. Conduction band E C    465  in region  480  between absorber  445  and barrier  440  presents a deeper notch in  FIG. 4  than in  FIG. 3  (notches at  480  and  380 , respectively). This implies a greater accumulation of majority carriers (electrons) between pixels than directly under them. As a corollary, there is a correspondingly greater shortage of minority carriers (holes) in notch  480  between the pixels in  FIG. 4  than in notch  380  under the pixels in  FIG. 3 , which simply means that minority holes will tend to collect under pixels rather than in the gaps between them. 
       FIG. 5  is a perspective view  500  of another embodiment of the overall FPA structure. Embodiments include a method of surface Fermi energy modulation comprising applying an electrostatic potential  590  voltage V1 to the metal pad  525  that defines each pixel and applying a different electrostatic potential  595  voltageV 2  to an interconnected metal grid  585  that covers the gaps between all the pixel metal pads  525 . Note that while voltage  590  V1 is applied to every metal pixel pad  525 , in  FIG. 5  it is depicted for only three adjacent metal pixel pads. This method is specifically analogous to the first method, except that the surface Fermi energy is now controlled, not by chemistry, but by externally applied voltages  590  and  595 . Detector structure comprises barrier  540  and absorber  545 . In embodiments, the metal pads are directly either on the barrier or on a cap layer above the barrier that facilitates a better electrical connection to the pixel. In embodiments, the grid metal is typically directly on the barrier, and typical values for  590  V1 are −0.5 volt and  595  V2=+1 volt. 
       FIG. 6  is a spectral response  600  of the focal plane material discussed in the context of the present embodiment. Sharp drop off  605  at half maximum shows a cutoff wavelength of 5.1 microns. Key to achieving this value is an absorber design using a Type II superlattice, in distinct contrast to the more traditional bulk InGaSb material lattice-matched to GaSb substrate, the cutoff wavelength of which is limited to 4.2 microns. The double-dip spectral feature  610  at 4.2-4.3 microns is due to carbon dioxide absorption, while multi-line spectral features  615  are attributable to water vapor absorption. Features  610  and  615  are environment artifacts that do not affect the position of cutoff  605  at 5.1 microns. 
       FIG. 7  is a plot  700  of the noise-equivalent temperature difference (NETD) measured in a representative focal plane array fabricated according to an embodiment of the invention. NETD is a performance metric commonly used to assess the level of temporal noise affecting an FPA. The figure shows that NETD  705  does not exceed 30 millikelvin (mK) up to an operating temperature of 130 K  710  with F/4 optics. The noise level increases above that temperature. For embodiments, by opening up the aperture to accept more photons, the upper limit of acceptable operating temperature is boosted to 150 K with F/2.5 optics. This data confirms the performance of FPAs fabricated by embodiments of this invention. This performance of FPA pixels defined by modulation of surface Fermi energy is state of the art, particularly in the midwave portion of the electromagnetic spectrum. 
       FIG. 8  shows graphically  800  that the spectrally averaged quantum efficiency  805  is essentially constant at around 85% over the entire temperature span from 80K to 150K. This parameter is derived from measurements of the total photocurrent generated upon exposure to an extended area blackbody source at a known temperature divided by the total photon flux at that source temperature spectrally integrated up to the cutoff wavelength. The high value of this quantum efficiency data additionally confirms the performance provided by the method of using modulation of the surface Fermi energy to define individual pixels. 
       FIG. 9  presents images  900  produced by embodiments of the invention. Operating temperatures of specific images are 80K  905 , 120K  910 , 130K  915 , 140K  920 , 150K  925 , 160K  930 , and 170K  935 . They illustrate how the quality of the images, captured here at F/ 4 , only gradually decreases with increasing operating temperature. One implication is that the 30 mK threshold is somewhat arbitrary. Significantly, the sharpness of the images obtained at the lower operating temperatures clearly demonstrates that (1) the technique described here to define individual pixels is quite immune to inter-pixel crosstalk in spite of the extremely shallow etch depths (only a couple of hundred Angströms) between pixels and (2) that it is conducive to high pixel operability. 
       FIG. 10  is a flow chart  1000  of an FPA fabrication method configured in accordance with one embodiment of the present invention. Steps comprise providing a substrate  1005 ; providing a common first contact layer  1010 ; providing an absorber layer  1015 ; providing barrier layer  1020 ; providing cap one layer  1025 ; providing cap two layer  1030 ; defining pixels by selectively etching cap two layer  1035 ; defining connection to common first contact layer  1040 ; providing metal contact layer to each pixel  1045 ; and providing metal contact layer to common first contact layer  1050 . 
     The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. Other and various embodiments will be readily apparent to those skilled in the art, from this description, figures, and the claims that follow. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.