BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of the photodiode according to a first embodiment of the present invention.
FIG. 2A is a plan view of a microlens array used in the photodiode shown in FIG. 1.
FIG. 2B is a side view of the microlens array used in the photodiode shown in FIG. 1.
FIG. 3A is a plan view of an alternative microlens array.
FIG. 3B is a side view of the alternative microlens array.
FIG. 4 is a schematic side view of the photodiode according to a second embodiment of the present invention.
FIG. 5 is a schematic side view of the photodiode according to a third embodiment of the present invention.
FIGS. 6A and 6B illustrate an operation of the photodiode shown in FIG. 5.
FIGS. 7A to 7H illustrate a method for manufacturing the photodiode shown in FIG. 5.
FIG. 8 is a schematic view of a lateral photodiode, illustrating the basic structure thereof.
FIG. 9 is a schematic side view of an example of conventional lateral photodiode.
FIG. 10 is a plan view of a comb electrode structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic side view of the lateral photodiode 10 according to a first embodiment of the present invention. As illustrated in the drawing, the photodiode 10 includes: a substrate 1; a semiconductor layer 2, formed on the substrate 1, for receiving input light L (detection target light); p-type regions 3 and n-type regions 4 formed parallel to the substrate 1 in the semiconductor layer 2; thin p-type electrodes 5, each connected to each p-type region 3; thin n-type electrodes 4, each connected to each n-type region; a transparent insulation layer 7 formed so as to cover the semiconductor layer from above; an electrode 8 which connects a plurality of p-type electrodes 5; and an electrode 9 which connects a plurality of n-type electrodes 6.
A microlens array 11 is formed on the insulation layer 7. FIG. 1 illustrates a side cross-section shape of the microlens array 11, and planar shape and side shape are like those illustrated in FIGS. 2A and 2B respectively. That is, the microlens array 11 includes a planar transparent plate 11b on which a plurality of microlenses 11a, having a substantially half-column shape, is arranged orthogonal to the long axis direction thereof, which is formed of a transparent material, such as optical glass, plastic, or the like.
The microlenses 11a of the microlens array 11 are arranged such that a boundary portion between them is located right above the p-type electrode 5 or n-type electrode 6, and edge portions of two microlenses 11a disposed in the right and left end portions are not disposed above the p-type electrodes 5. The light receiving area of the lateral photodiode 10 substantially corresponds to the area where the entire microlens array 11 is extended.
In the lateral photodiode 10 of the present embodiment structured in the manner as described above, the input light L traveling toward the semiconductor layer 2 is focused in a manner so as not to be directed toward the p-type electrodes 5 and n-type electrodes 6 by each of the microlenses 11a of the microlens array 11, as illustrated in FIG. 1. Note that the microlens 11a of the present embodiment is so-called the cylindrical lens, so that the input light L is focused only in the plane of FIG. 1 and not in the direction orthogonal to the plane. The focusing of the input light L in the manner as described above may prevent the input light L from being absorbed by the p-type electrodes 5 and n-type electrodes 6, so that the light receiving efficiency is increased and high sensitivity of the lateral photodiode 10 is realized.
Note that the p-type electrodes 5 and n-type electrodes may be formed in an appropriate shape according to the arrangement of the p-type regions 3 and n-type regions 4. Further, such p-type electrodes 5 and n-type electrodes 6 may form a comb electrode structure like that illustrated in FIG. 10. In this case, the effect of sensitivity improvement is significant as described above.
Further, instead of the microlens array 11 formed of a plurality of microlenses 11a, which are cylindrical lenses, a microlens array 12 that includes a planar transparent plate 12b on which a plurality of substantially hemispherical microlenses 12a is disposed as illustrated in FIGS. 3A and 3B may be used. The use of the microlens array 11 results in low power density of the focused light in comparison with the use of the microlens array 12, since the light is focused only in one-dimensional direction. Consequently, the use of the microlens array 11 allows reception of input light L having higher power in comparison with the use of the microlens array 12.
A second embodiment of the present invention will now be described with reference to FIG. 4. In FIG. 4, elements identical to those in FIG. 1 are given the same reference numerals and will not be elaborated upon further here unless otherwise specifically required (the same applies hereinafter).
In a photodiode 20 according to the second embodiment, a plurality of microlenses 7a is formed on the surface portion of the transparent insulation layer 7. Each of the microlenses 7a is formed in the portion between each of the p-type electrodes 5 and n-type electrodes 6, and focuses the input light L in a manner so as not to be directed to the p-type electrodes 5 and n-type electrodes 6, as in the microlenses 11a in FIG. 1. Therefore, in this case also, the input light L is prevented from being absorbed by the p-type electrodes 5 and n-type electrodes 6, so that the light receiving efficiency is increased and high sensitivity of the lateral photodiode 20 is realized.
In the present embodiment, the input light L incident normal to the upper surfaces of the p-type electrodes 5 and n-type electrodes 6 may not be prevented from being absorbed by the electrodes. In this case, however, the light incident on the side faces of the p-type electrodes 5 and n-type electrodes 6, like the guided light Lg shown in FIG. 9 or the like, may be focused, and absorption by the electrodes may be prevented. Further, not limited to such guided light Lg, if a component traveling at an angle is included in the input light L, then such component may be prevented from being absorbed from the side faces of the p-type electrodes 5 and n-type electrodes 6.
Next, a third embodiment of the present invention will be described with reference to FIG. 5. The photodiode 30 according to the third embodiment differs from the photodiode 20 shown in FIG. 4 in that it also includes microlenses 2a on the surface portion of the semiconductor layer 2, each between each of the p-type electrodes 5 and n-type electrodes 6.
In the photodiode 30 also, high sensitivity is realized by the microlenses 7a formed on the surface portion of the transparent insulation layer 7. In addition, the microlenses 2a formed on the surface portion of the semiconductor layer 2 provide further advantageous effects, which will be described in detail below.
FIG. 6A schematically illustrates a carrier movement path between each of the p-type electrodes 5 and n-type electrodes 6 in the case where the microlens 2a is not provided, while FIG. 6B schematically illustrates the carrier movement path in the case where the microlens 2a is provided. The carrier movement path is represented by the bold-line arrows in the drawings. When the microlens 2a is not provided, the carrier movement path is like that illustrated in FIG. 6A, while if the microlens 2a is provided, the input light L is focused to high power on a position closer to the surface of the semiconductor layer 2. Consequently, more carriers are formed at a position closer to the surface of the semiconductor layer 2 and move to the electrodes 5 and 6 rapidly, resulting in a high-speed response.
Next, a manufacturing method of the photodiode 30 will be described with reference to FIGS. 7A to 7H. Note that process steps A to H described hereinafter correspond to FIGS. 7A to 7H respectively. First, in step A, a substrate 1 is provided. Then, in step B, a plurality of protrusions 40 is formed, for example, by CVD method on the substrate 1. Next, in step C, the semiconductor layer 2 is stacked thereon, and further, in step D, the transparent insulation layer is stacked on the semiconductor layer 2. This causes microlenses 2a and 7a raised according to the protrusions 40 to be formed on the surfaces of the semiconductor layer 2 and transparent insulation layer 7 respectively. The shape of the protrusion 40 may be selected according to a desired shape of the microlens to be formed, such as rectangular shape, spindle shape, or the like.
Then, in step E, a plurality of holes 41 is created in the transparent insulation layer 7 at positions between the microlenses 2a and 7a by, for example, photolithography and etching process, and a polysilicon layer 42 is formed on the transparent insulation layer 7. Then, in step F, the p-type electrodes 5 and n-type electrodes 6 are sequentially formed in the holes 41 by ion implantation. At this time, the p-type regions 3 and n-type regions 4 are also formed in the semiconductor layer 2. Then, in step G, the polysilicon layer 42 is removed, and, in step H, electrodes 8 and 9 are formed. This completes the manufacture of the photodiode 30 described above.
When providing another layer which includes microlenses on the transparent insulation layer 7, a separately provided microlens array or the like may be attached on the transparent insulation layer 7 as in the first embodiment, or the layer may be formed on the transparent insulation layer 7 through successive stacking processes. When forming such a layer by the latter method, microlenses may be formed on the layer using the protrusions 40 described above.
In the manufacturing method described above, a plurality of protrusions 40 is provided to form microlenses 2a raised according to the protrusions (which, in turn, serve as the protrusions for forming the microlenses 7a), and microlenses 7a. Thus, a plurality of microlenses 2a and 7a is formed easily, and the high sensitivity lateral photodiode 30 is manufactured efficiently. As example materials, the following may be used: silicon for the substrate 1, germanium for the semiconductor layer 2, oxide silicon for the transparent insulation layer 7, and aluminum for the electrodes 8 and 9.
Patent Application
20080023781
