Abstract:
This invention is directed toward a method for manufacturing a semiconductor device with a heterostructure comprises covering a semiconductor structure with a seed layer structure; forming one or more separated circularly shaped openings in the seed layer structure to expose the semiconductor structure therein, and leave the seed layer structure outside the one or more separated circularly shaped openings; forming an insulator layer thereon; etching the obtained structure to (i) expose at least a portion of the seed layer structure, such that the exposed at least portion of the seed layer structure surrounds each of the one or more separated circularly shaped openings, and (ii) optionally expose the semiconductor structure, in the one or more separated circularly shaped openings; and epitaxially growing a semiconductor layer from the exposed at least portion of the seed layer structure, firstly mainly vertically and then into each of the one or more separated circularly shaped openings until the epitaxially grown semiconductor layer coalesces with the insulator layer or the semiconductor structure in each of the one or more separated circularly shaped openings.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to semiconductor device technology, and particularly to methods for manufacturing a semiconductor device and to semiconductor device. 
       DESCRIPTION OF RELATED ART 
       [0002]    WO 2013/154485 discloses a method for manufacturing a semiconductor device comprising the steps of: forming a buffer layer and a seed layer on a dissimilar semiconductor substrate on a front side thereof, followed by processing to provide one or more seed island mesas, typically having a particular orientation on the dissimilar semiconductor substrate. An insulating layer is then formed on the at least one seed island mesa and an opening is created in the insulating layer. Then a semiconductor growth layer having consecutive semiconductor regions grown onto each other is grown from the opening of the insulating layer. The growth is selective: epitaxially, vertically and laterally, wherein a first region having high defect density is only grown vertically from the opening, while the other regions are grown until at least one semiconductor region having low defect density coalesces with the front side of the semiconductor substrate. The first region and a second region of the semiconductor growth layer with high defect density can be removed by etching and a third region with low defect density is not etched, typically protected from etching to prepare a semiconductor layer for semiconductor device fabrication. In this way, a semiconductor device having a hetero-structure, for instance a semiconductor substrate, with low defect density can be manufactured on a dissimilar substrate. 
         [0003]    However, a drawback with the method is the seed island mesas have to be formed in a particular orientation with respect to the crystal direction of the semiconductor substrate to maximize the aspect ratio between the laterally grown third region with low defect density and the vertical growth. This may add processing time and costs to the manufacturing process. 
         [0004]    A further drawback is that dislocations may occur in the epixatially grown semiconductor layer in regions where growth fronts meet between two mesas. 
         [0005]    Another design is disclosed in U.S. Pat. No. 8,299,502, which, however, does not disclose the use of seed island mesas. A semiconductor heterostructure includes a crystalline substrate of a first semiconductor material and a mask disposed over a surface of the crystalline substrate. The mask has openings including a plurality of elongated opening sections with a width less than or equal to 900 nm. At least one first section of the elongated opening sections is directed non-parallel relative to at least one second section of the elongated opening sections. The semiconductor heterostructure further includes an overgrowth crystalline layer of a second semiconductor material, filling the openings and covering the mask. A method for manufacturing of such a semiconductor heterostructure is also disclosed. 
       SUMMARY OF THE INVENTION 
       [0006]    The present inventor has found a novel design for semiconductor heterostructures with epitaxially overgrown semiconductor layers, which can be applied both for seed island mesas and planar seed layers. 
         [0007]    In one aspect, a method for manufacturing a semiconductor device with a heterostructure is provided, according to which a semiconductor structure including a semiconductor substrate is covered with a seed layer structure. One or more separated circularly shaped openings is/are formed in the seed layer structure to expose the semiconductor structure therein, while the seed layer structure is left outside the one or more separated circularly shaped openings. An insulator layer is formed thereon, after which the obtained structure is etched to (i) expose the surface at least a portion of the seed layer structure, such that the exposed at least portion of the seed layer structure surrounds each of the one or more separated circularly shaped openings, and (ii) optionally expose the surface of semiconductor structure, in the one or more separated circularly shaped openings. Next, a semiconductor layer is epitaxially grown from the surface exposed at least portion of the seed layer structure, firstly mainly vertically and then into each of the one or more separated circularly shaped openings until the epitaxially grown semiconductor layer coalesces with the insulator layer or the semiconductor structure in each of the one or more separated circularly shaped openings, to thereby form a uniform continuous grown semiconductor layer sections in each of the one or more separated circularly shaped openings. 
         [0008]    Hereby, the epitaxially grown semiconductor layer forms a first region having a first defect density during the mainly vertical growth and a second region having a second defect density during the growth in each of the one or more separated circularly shaped openings, wherein the second defect density is lower, preferably much lower, than the first defect density. 
         [0009]    For instance, the second defect density may be lower than 10 8 , 10 7 , 10 6 , or 10 5  cm −2 , whereas the first defect density may be higher than 10 5 , 10 6 , 10 7 , or 10 8  cm −2 . The exposed at least portion of the seed layer structure, from which the semiconductor layer is epitaxially grown, can have a third defect density, which may be in the same order of magnitude as the first defect density. 
         [0010]    While the circularly shaped openings may be arranged with respect to one another in any fashion, one embodiment comprises a design with circularly shaped openings arranged with rows and columns in a two-dimensional pattern, wherein the circularly shaped openings of every second row is arranged displaced in the direction of the row such that the circularly shaped openings of every column are arranged in a staggered pattern. Hereby, the area of the mesa structure can be minimized. 
         [0011]    The method is straightforward and the mesa structure surrounding the circularly shaped openings has not to be formed in a particular orientation with respect to the crystal direction of the semiconductor substrate to maximize the lateral overgrowth in openings. 
         [0012]    Further, the amount of dislocations in the epixatially grown semiconductor layer is minimized in regions where growth fronts meet between because such growth fronts will not meet along a line but in a single point (in each of the one or more separated circularly shaped openings). 
         [0013]    The epitaxially grown semiconductor layer may be an n-type, p-type, or semi-insulating doped semiconductor layer. The material of the epitaxially grown semiconductor layer and the seed layer structure (or seed layer thereof) may be a III-V semiconductor, e.g. InP or GaAs, or a ferromagnetic III-V semiconductor, e.g. GaMnAs, InMnAs, or similar. The semiconductor structure or substrate may be of different doping type than the epitaxially grown semiconductor layer. 
         [0014]    Texture may be formed in or above the semiconductor structure or substrate and/or doped silicon areas may be formed in or above the semiconductor structure or substrate within the one or more separated circularly shaped openings before the insulator layer is formed e.g. depending on the semiconductor device to be manufactured. 
         [0015]    In one embodiment, the step of etching comprises patterning and etching using photolithographic techniques to expose at least a portion of the seed layer structure, such that the exposed at least portion of the seed layer structure surrounds each of the one or more separated circularly shaped openings. The etching may comprise etching away the insulator layer in the one or more separated circularly shaped openings to expose the surface of semiconductor structure and the epitaxial growth of the semiconductor layer may be performed until the epitaxially grown semiconductor layer coalesces with the semiconductor structure in each of the one or more separated circularly shaped openings and forms a uniform continuous layer in each of the one or more separated circularly openings. 
         [0016]    Alternatively, the insulator layer is left in the one or more separated circularly shaped openings in the etching and the epitaxial growth of the semiconductor layer is performed until the epitaxially grown semiconductor layer coalesces with the insulator layer in each of the one or more separated circularly shaped openings and forms a uniform continuous layer in each of the one or more separated circularly openings. 
         [0017]    In another embodiment, the portions of the insulator layer on top of the seed layer structure are removed by anisotropic etching in a self-aligned process leaving the insulator layer only as side walls on the sides of the seed layer structure in each of the one or more separated circularly shaped openings. 
         [0018]    By such procedure, the separated circularly shaped openings may be arranged closer to another while providing sufficient seeding surfaces for the epitaxial growth. The self-aligned positions of these seeding surfaces do not require safety distances for misalignments in the photolithographic process otherwise employed. The self-aligned process provides for a minimum of unusable area (which is not seeding layer area or area, in which epitaxial growth layer for device manufacturing is formed (circularly shaped openings)). 
         [0019]    In a second aspect, a method for manufacturing a semiconductor device with a heterostructure is provided, according to which a semiconductor structure is covered with a seed layer structure. An insulator layer is formed thereon and portions of the insulator layer are removed to expose portions of the seed lay structure, while one or more separated circularly shaped portions of the insulator layer is/are left on the seed layer structure. A semiconductor layer is epitaxially grown from the exposed portions of the seed layer structure, firstly mainly vertically and then onto each of the one or more separated circularly shaped portions of the insulator layer until the epitaxially grown semiconductor layer coalesces with the insulator layer in each of the one or more separated circularly shaped portions of the insulator layer. 
         [0020]    Hereby, the epitaxially grown semiconductor layer may form a first region having a first defect density during the mainly vertical growth and a second region having a second defect density during the growth onto each of the one or more separated circularly shaped portions of the insulator layer, wherein the second defect density is lower than the first defect density. 
         [0021]    Example figures of the first and second defect densities and of the defect density of the exposed portions of the seed lay structure may be as given above. 
         [0022]    The first and second aspects may be further modified according to the below. 
         [0023]    The seed layer structure may be a single seed layer, or a multilayer comprising e.g. a buffer layer and a seed layer on top of the buffer layer. 
         [0024]    The semiconductor structure referred to as a start material above may comprise a semiconductor substrate and optionally one or more layers thereon such as for instance a semiconductor layer and/or an insulator layer. The term heterostructure refers to that the substrate and the epitaxially grown semiconductor layer, which is of the same material as the seed layer, are of different materials. 
         [0025]    The seed layer may be of a III-V semiconductor material, such as e.g. a material comprising InP, whereas the substrate of the semiconductor structure is of another material, such as a IV semiconductor material, e.g. silicon. 
         [0026]    In one embodiment, the one or more separated circularly shaped openings or the one or more separated circularly shaped portions of the insulator layer are a plurality. The shortest distance between each two adjacent separated circularly shaped openings or two separated circularly shaped portions of the insulator layer may be less than 4, 3, 2 or 1 μm. 
         [0027]    One electronic component, preferably active electronic component, may be formed from the epitaxially grown semiconductor layer grown in each of the one or more separated circularly shaped openings or on top of each of the one or more separated circularly shaped portions of the insulator layer. In such instance, the semiconductor structure or substrate and the epitaxially grown semiconductor layer may be of different doping type. For instance, the semiconductor structure may be of n-doping type and the epitaxially grown semiconductor layer may be of p-doping type. 
         [0028]    Alternatively, several electronic components, preferably active electronic components, are formed from the epitaxially grown semiconductor layer grown in each of the one or more separated circularly shaped openings or on top of each of the one or more separated circularly shaped portions of the insulator layer. 
         [0029]    The one or several electronic components may each be a solar cell, a laser diode, or a light sensitive component such as a photodiode or avalanche photodiode. 
         [0030]    A third aspect refers a semiconductor device manufactured according to any of the methods disclosed above. 
         [0031]    A fourth respect refers to a semiconductor device comprising a semiconductor structure, one or more separated circularly shaped layer portions of an epitaxial semiconductor on the semiconductor structure, and one or more electronic components, preferably active electronic components, such as e.g. solar cells, laser diodes, or light sensitive components, such as photodiodes or avalanche photodiodes, formed at least partly in each of the one or more circularly shaped layer portions of an epitaxial semiconductor. 
         [0032]    An insulator may covers the outer sidewalls of each of the one or more circularly shaped layer portions of an epitaxial semiconductor and a seed layer structure may cover the spaces between the one or more circularly shaped layer portions of an epitaxial semiconductor having outer sidewalls covered by an insulator. 
         [0033]    A fifth aspect refers to a semiconductor device comprising semiconductor structure or substrate, a seed layer structure thereon, one or more separated circularly shaped layer portions of an insulator thereon, an epitaxial semiconductor layer on top of the one or more separated circularly shaped layer portions of an insulator, and one or more electronic components, preferably active electronic components, such as e.g. solar cells, laser diodes, or light sensitive components, such as photodiodes or avalanche photodiodes, formed at least partly in the epitaxial semiconductor layer on top of each of the one or more separated circularly shaped layer portions of an insulator. 
         [0034]    The one or more separated circularly shaped openings (the first and third aspects), the one or more separated circularly shaped portions of the insulator layer (the second and third aspects), the one or more separated circularly shaped layer portions of an epitaxial semiconductor (fourth aspect), and the one or more separated circularly shaped layer portions of an insulator on the seed layer structure (the fifth aspect) may have a diameter in the range of 1-100 microns. 
         [0035]    Another challenge with the teaching of WO 2013/154485 is that the opening made in the insulating layer on top of the seed island mesas to expose portions thereof is time consuming and requires a safety margin, which in turn creates an unusable area between the expose portions of the seed island mesas and the exposed portions of the substrate. 
         [0036]    A sixth aspect refers to method for manufacturing a semiconductor device with a heterostructure. According to the method a semiconductor structure or substrate is covered with a seed layer structure and one or more openings is/are formed in the seed layer structure to expose the semiconductor structure therein. An insulator layer is formed thereon and portions of the insulator layer are removed by anisotropic etching in a self-aligned process leaving the insulator layer only as side walls in each of the one or more openings. Thereafter, a semiconductor layer is epitaxially growing from the exposed portions of the seed layer structure, firstly mainly vertically and then into each of the one or more openings until the epitaxially grown semiconductor layer coalesces with the semiconductor structure in each of the one or more openings. Before the epitaxial growth, the exposed portions of the seed layer may be chemically cleaned or wet etched to reduce the thickness of seed structure. 
         [0037]    The one or more openings may each be formed as a stripe shaped opening e.g. aligned at an angle off the major flat direction on the semiconductor structure or substrate to maximize the lateral overgrowth in the one or more openings. 
         [0038]    Alternatively, the one or more openings may each be formed as a circularly shaped opening or square shaped opening, optionally with rounded corners. 
         [0039]    The width of each stripe shaped opening, the diameter of each circularly shaped opening, and/or the side length of each square shaped opening may be in the range of 10-100 microns. 
         [0040]    A seventh aspect refers to a semiconductor device manufactured according to the method of the sixth aspect. 
         [0041]    Hereby, the one or more openings may be arranged closer to another while providing sufficient seeding surfaces for the epitaxial growth. The distance between the openings can be smaller than 4, 3, 2, 1 or 0.5 μm. The self-aligned positions of these seeding surfaces do not require safety distances for misalignments in the photolithographic process otherwise employed. The self-aligned process provides for a minimum of unusable area. 
         [0042]    The epitaxially grown semiconductor layer may be an n-type, p-type, or semi-insulating doped semiconductor layer. The material of the epitaxially grown semiconductor layer and a the seed layer structure (or seed layer thereof) may be a III-V semiconductor, e.g. InP or GaAs, or a ferromagnetic III-V semiconductor, e.g. GaMnAs, InMnAs, or similar. Further characteristics and advantages will be evident from the following detailed description of embodiments given hereinafter and the accompanying  FIGS. 1-7 , which are given by way of illustration only, and are thus not limitative. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIGS. 1 a - g    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a first embodiment.  FIGS. 1 a - b  and  d - g    are side sectional views while  FIG. 1 c    is a top view. 
           [0044]      FIG. 2  illustrates schematically, in a side sectional view, a semiconductor device with a heterostructure during manufacturing according to a second embodiment. 
           [0045]      FIGS. 3 a - c    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a third embodiment.  FIGS. 3 a - b    are side sectional views while  FIG. 3 c    is a top view. 
           [0046]      FIGS. 3 d - f    illustrate schematically a semiconductor device in a side sectional view with a heterostructure during manufacturing according to variants of the third embodiment. 
           [0047]      FIGS. 4 a - d    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a fourth embodiment.  FIGS. 4 a - b  and  d    are side sectional views while  FIG. 4 c    is a top view. 
           [0048]      FIG. 5  illustrates schematically a semiconductor device in a side sectional view with a heterostructure according to an embodiment. 
           [0049]      FIGS. 6 a - b    illustrate schematically a semiconductor device with a heterostructure according to a further embodiment.  FIG. 6 a    is a side sectional view, whereas  FIG. 6 b    is a sectional view along line A-A of  FIG. 6   a.    
           [0050]      FIGS. 7 a - b    illustrate schematically a semiconductor device with a heterostructure according to a yet further embodiment.  FIG. 7 a    is a side sectional view, whereas  FIG. 7 b    is a sectional view along line A-A of  FIG. 6   a.    
       
    
    
       [0051]    Identical reference numerals are used throughout the Figures to denote identical or similar components, portions, details and the like of the various embodiments. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0052]      FIGS. 1 a - g    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a first embodiment. 
         [0053]    A semiconductor structure  50  is covered by a seed layer structure  52 ,  54 . 
         [0054]    The semiconductor structure  50  comprises a substrate, which may be of a IV semiconductor material, e.g. (001) silicon. 
         [0055]    The seed layer structure  52 ,  54  may comprise a buffer layer  52  made of, for example GaAs, formed, for instance grown, on the semiconductor structure  50 , by metalorganic vapor phase epitaxy (MOVPE) at low temperature, and a seed layer  54  made of a III-V semiconductor material, for example InP is grown by MOVPE and can have a thickness of approximately 2 μm. Alternatively, the seed layer structure is composed of a single seed layer. 
         [0056]    A protective mesa mask  56  made of, for example SiO 2  or SiN x  is deposited by plasma-enhanced chemical vapor deposition (PECVD) and patterned by photolithography and dry etching, for example reactive ion etching or inductively coupled plasma etching, or by chemical etching in HF solution. Typically, the protective mesa mask  56  can have thickness of more than 300 Å and a width corresponding to a desired mesa width. The resulting structure is shown in  FIG. 1   a.    
         [0057]    The seed layer structure (the seed layer  54  and the buffer layer  52 ) is processed using the protective mesa mask  56  to form a mesa structure  51  typically by dry etching. The resulting structure is shown in  FIG. 1 b   . The protective mesa mask  56  is so shaped that, one or more separated circularly shaped openings  53  are formed in the seed layer structure  52 ,  54  to expose the semiconductor structure  50  therein, and leave the seed layer structure  52 ,  54  outside the one or more separated circularly shaped openings  53 .  FIG. 1 c    illustrates schematically the structure from above. 
         [0058]    Note that while  FIG. 1 c    illustrates  14  circularly shaped openings  53  in three rows and the side sectional view of  FIG. 2  in  FIG. 1 b    only illustrates one circularly shaped opening  53  in the center and parts of two further circularly shaped openings  53  in the left-hand and right-hand ends of the Figure, the concept may be used for manufacturing a semiconductor device with any number of circularly shaped openings. Further, the circularly shaped openings  53  may arranged with respect to one another in any fashion even though the illustrated design with the circularly shaped openings  53  of every second row being displaced in the direction of the row such that the circularly shaped openings  53  in each column is arranged in a staggered manner to minimize the area of the mesa structure  51 . 
         [0059]    The shortest distance between two adjacent separated circularly shaped openings  53  may be less than 4 μm, preferably less than 3 μm, more preferably less than 2 μm, and most preferably less than 1 μm. 
         [0060]    The diameter of each of the adjacent separated circularly shaped openings  53  may be 10-100 μm, but can be smaller than 10 μm or larger than 100 μm. 
         [0061]    Next, an insulating layer  62  made of, for example Si 3 N 4 , is formed over the semiconductor structure  50  and the protective mesa mask  56 , and is typically deposited by PECVD. The insulating layer  62  can have a thickness of more than 300 Å. The resulting structure is shown in  FIG. 1   d.    
         [0062]    The insulating layer  62  is etched e.g. by SF 6  and CH 4  in a reactive ion etching reactor. Chemical CHF 3  can alternatively be used to etch the insulating layer  62  in the reactive ion etching reactor. The insulating layer  62  is etched away completely from the top surface  60  of the protective mesa mask  56 ) of the mesa structure  51  and the semiconductor structure  50 , whereas the insulating layer  62  on the side walls in each of the one or more separated circularly shaped opening  53  is protected, for instance by polymers formed during etching and an anisotropic etching mechanism and is intact after etching. As a result, the top surface  60  of the mesa structure  51  and the front side  50   a  of the semiconductor structure  50  are exposed as shown in  FIG. 1 e   . An opening  58  is patterned by photolithography and etched through the protective mesa mask  56  to expose a portion of the seed layer  54  of the seed layer structure  52 ,  54 . The resulting structure is shown in  FIG. 1   f.    
         [0063]    Next, a semiconductor layer  80  is epitaxially grown from the exposed portion of the seed layer  54 , firstly mainly vertically and then into each of the one or more separated circularly shaped openings  53  until the epitaxially grown semiconductor layer  80  coalesces with the semiconductor structure  50  in each of the one or more separated circularly shaped openings  53  and forms a uniform continuous layer in each of the one or more separated circularly shaped openings  53 . 
         [0064]    The growth of the epitaxial layer  80  may be carried out using Hydride Vapor Phase Epitaxy (HVPE) or other epitaxial growth methods operated at equilibrium condition providing selectivity of III-V growth over Si, SiO 2  and SiN x  surfaces. The front side  50   a  of the semiconductor structure  50  made of, for example Si, is cleaned properly before the structure is brought to an HYPE growth chamber. A solution of H 2 SO 4 :H 2 O 2  and NH 4 OH:H 2 O 2  may be used to remove the organic impurities and particles. Following a wet chemical ex-situ cleaning process, the semiconductor structure  50  may be dipped in a solution of 1 HF: 10 H 2 O for 10 seconds to remove oxide. As an example, the growth temperature in the HVPE growth chamber may be 620° C. and the pressure may be 20 mBar. With sufficient growth time, which is obvious to a skilled person, the selective growth from the mesa structure  51  will result in wide third semiconductor regions, which will coalesce to form the continuous grown semiconductor layer portion(s)  80  on the front side  50   a  of the semiconductor structure  50 . The resulting structure is shown in  FIG. 1   g.    
         [0065]    The epitaxially grown semiconductor layer forms a first region Boa having a first defect density during the mainly vertical growth and a second region Bob having a second defect density during the growth in each of the one or more separated circularly shaped openings  53 , wherein the second defect density will preferably be lower than the first defect density. 
         [0066]    The second defect density may be lower than 10 8  cm −2 , preferably lower than 10 7  cm −2 , more preferably lower than 10 6  cm −2 , and most preferably lower than 10 5  cm −2 , whereas the first defect density may be higher than 10 5  cm −2 , preferably higher than 10 6  cm −2 , more preferably higher than 10 7  cm −2 , and most preferably higher than 10 8  cm −2 . 
         [0067]    The exposed of the seed layer  54  has a third defect density, which may be in the same order of magnitude as the first defect density. 
         [0068]    The epitaxially grown semiconductor layer  80  may be an n-type, p-type, or semi-insulating doped semiconductor layer. The material of the epitaxially grown semiconductor layer and the seed layer  54  may be a III-V semiconductor, e.g. InP or GaAs, or a ferromagnetic III-V semiconductor, e.g. GaMnAs, InMnAs, or similar. 
         [0069]    The processing may then be continued as disclosed in WO 2013/154485, e.g. by removing the upper part of the epitaxially grown semiconductor layer  80  to expose the remaining portion of the protective mesa mask  56  and the upper surface of the insulating layer  62  on the side walls in each of the one or more separated circularly shaped openings  53 , and then removing the remaining portion of the protective mesa mask  56 , the insulating layer  62  on the side walls in each of the one or more separated circularly shaped openings  53 , and the seed layer structure  52 ,  54  to form one or more separated circularly shaped layer portions of the epitaxially grown semiconductor layer  80 , is which device formation can take place. The contents of WO 2013/154485 is hereby incorporated by reference. 
         [0070]    In one variant, one electronic component, preferably active electronic component, is formed from the epitaxially grown semiconductor layer  80  grown in each of the one or more separated circularly shaped openings  53 . 
         [0071]    In another variant, several electronic components, preferably active electronic components, are formed from the epitaxially grown semiconductor layer  80  grown in each of the one or more separated circularly shaped openings  53 . 
         [0072]    The one or several electronic components may each be a solar cell, a laser diode, or a light sensitive component, such as a photodiode or an avalanche photodiode. 
         [0073]      FIG. 2  illustrates schematically, in a side sectional view, a semiconductor device with a heterostructure during manufacturing according to a second embodiment, which is identical with previous embodiment up to the formation of the one or more separated circularly shaped openings  53  in the seed layer structure  52 ,  54  using the protective mesa mask  56 . Subsequently, thereto the mesa mask  56  is removed by chemical etching in HF solution, and an insulating layer  72 , made for instance of Si 3 N 4 , is deposited on the obtained structure by for instance PECVD. Then, openings  58   b  are etched in the insulating layer  72  to expose a portion of the seed layer  54  of the seed layer structure  52 ,  54 . Thereafter, a semiconductor layer  80  is epitaxially grown from the exposed portion of the seed layer  54 , firstly mainly vertically and then into each of the one or more separated circularly shaped openings  53  until the epitaxially grown semiconductor layer  80  coalesces with the insulating layer  72  in each of the one or more separated circularly shaped openings  53  and forms a uniform continuous grown layer  80  in each of the one or more separated circularly shaped openings  53 . The epitaxial growth may be performed as disclosed above with reference to the embodiment of  FIGS. 1 a   - g.    
         [0074]    The processing may then continue as disclosed above. The main difference between the  FIGS. 1 and 2  embodiments is that when the epitaxially grown semiconductor layer  80  is formed on top of a semiconductor structure, e.g. a semiconductor substrate, in the embodiment of  Figs. 1 a - g   , whereas the epitaxially grown semiconductor layer  80  is formed on top of an insulator layer in the embodiment of  FIG. 2 . 
         [0075]      FIGS. 3 a - c    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a third embodiment, which is identical with the embodiment of  FIGS. 1 a - g    up to the formation of the one or more separated circularly shaped openings  53  in the seed layer structure  52 ,  54  using the protective mesa mask  56 . Subsequently, thereto the mesa mask  56  is removed, and an insulating layer  72 , made for instance of Si 3 N 4 , is deposited on the obtained structure by for instance PECVD. The resulting structure is shown in  FIG. 3   a.    
         [0076]    Then, the insulating layer  72  is etched anisotropically e.g. without using a mask, in a self-aligned process exposing the seed layer  54  of the seed layer structure  52 ,  54  and the semiconductor structure  50  in the separated circularly shaped openings  53 , and leaving the insulating layer  72  only a sidewall spacers in the separated circularly shaped openings  53 , in a self-aligned process. The resulting structure is shown in  FIGS. 3 b    (side sectional view) and  3   c  (top view). In  FIG. 3 c   , the upper surface of the seed layer structure  58   b  and the annular shaped sidewall spacers  72  within the separated circularly shaped openings  53  are clearly apparent. The exposed portion of the seed layer  54  of the seed layer structure  52 ,  54  is self aligned to the sidewall spacers of the insulating layer  72 . 
         [0077]    Thereafter, a semiconductor layer is epitaxially grown from the exposed seed layer  54 , optionally after chemically cleaning or wet chemical etching to reduce the thickness of the seed layer  54 , firstly mainly vertically and then into each of the separated circularly shaped openings  53  until the epitaxially grown semiconductor layer coalesces with semiconductor substrate  50  in each of the separated circularly shaped openings  53  and the further processing may then continue as disclosed above. The main difference between the  FIGS. 1 and 3  embodiments is that when the epitaxially grown semiconductor layer  80  is grown from a portion only of the seed layer  54  of the seed layer structure  52 ,  54  as shaped by photolithographic technology in the embodiment of  FIGS. 1 a - g   , whereas the epitaxially grown semiconductor layer is grown from a the entire seed layer  54  of the seed layer structure  52 ,  54  in the embodiment of  FIGS. 1 a   - g.    
         [0078]    The further processing may be performed as disclosed with reference to the embodiment of  FIGS. 1 a   - g.    
         [0079]    The semiconductor structure  50  may consist of a semiconductor substrate, optionally with one or more semiconductor layers thereon. 
         [0080]    Alternatively, the epitaxially grown semiconductor layer is formed on an insulator layer and not on a semiconductor. After the formation of the one or more separated circularly shaped openings  53  in the seed layer structure  52 ,  54  using the protective mesa mask  56 , but before the removal of the mesa mask  56 , a further insulator layer of different material than the mesa mask  56  may be deposited. The mesa mask  56  may be of Si 3 N 4  whereas the further insulator layer may be of Al 2 O 3 . Examples of resulting structures are shown in  FIGS. 3 d  and 3 e    for different shapes of the seed layer structure  52 ,  54 . The further insulating layer, denoted by  301 , may be deposited by e-beam evaporation. 
         [0081]    Subsequent thereto, the mesa mask  56  is removed by selective etching using e.g. H 3 PO 4 , which will not etch the Al 2 O 3  layer  301 . When the Si 3 N 4  layer  56  on top of mesa structure  52 ,  54  is removed, also the Al 2 O 3  layer  301  section on top of the Si 3 N 4  layer  56  is removed in a lift off process. Thereby, an exposed, clean mesa surface is obtained. The process is self-aligned without requirement of lithography. The lift off process is facilitated by a shape of the seed layer structure  52 ,  54  as shown in  FIG. 3   e.    
         [0082]    Thereafter, the insulator layer  72  is then deposited on the obtained structure by for instance PECVD, the resulting structure of which being shown in  FIG. 3 a   . The process then continues as disclosed with reference to  FIGS. 3 a   - c.    
         [0083]    Alternatively, using the shape of the seed layer structure  52 ,  54  as shown in  FIG. 3 d   , engineering the shape of the mesa mask  56  to assist the lift off process, and depositing the further insulator layer  301  by e-beam evaporation, a structure as shown in  FIG. 3 f    is obtained. 
         [0084]    Then, the mesa mask  56  is removed by selective etching using e.g. H 3 PO 4 , wherein also the further insulator layer  301  section on top of the mesa mask  56  is removed in a lift off process. As a result, the further insulator layer  301  remains not only on the semiconductor structure  50 , but also as sidewall spacers in the separated circularly shaped openings  53 , in a self-aligned process. Hereby, the deposition and self-aligned etching of the insulator layer  72  can be dispensed with, and the process can continue with the semiconductor layer being epitaxially grown from the exposed seed layer  54  of the seed layer structure  52 ,  54  as disclosed above. 
         [0085]    The shapes of the one or more openings  53  may be different than what is disclosed in  FIG. 3 c   . Each of the one or more openings  53  may be formed as a stripe shaped opening e.g. aligned at an angle, e.g. 30°, off the [110] direction on a (001) substrate to maximize the lateral overgrowth in the one or more openings, or as square shaped opening optionally with rounded corners. The distance between the openings can be smaller than 4, 3, 2, 1 or 0.5 μm. 
         [0086]    More generally, the one or more openings may each be formed as a stripe shaped opening aligned at an angle off the major flat direction on the semiconductor structure or substrate to maximize the lateral overgrowth in the one or more openings. 
         [0087]    A layout with such stripe shaped openings is illustrated in WO 2013/154485 A1. 
         [0088]      FIGS. 4 a - d    illustrate schematically a semiconductor device with a heterostructure during manufacturing according to a fourth embodiment.  FIGS. 4 a - b  and  d    are side sectional views while  FIG. 4 c    is a top view. A semiconductor structure  81  is covered with a seed layer structure  82 , and an insulator layer  83  is formed thereon. The resulting structure is shown in  FIG. 4   a.    
         [0089]    Portions of the insulator layer  83  are removed to form openings  84  in the insulator layer  83  to expose portions of the seed lay structure  82 , while one or more separated circularly shaped portions  85  of the insulator layer  83  is/are left on the seed layer structure  82 . The resulting structure is shown in  FIGS. 4 b  and  c   . In  FIG. 4 c   , the openings  84  to expose the portions of the seed lay structure  82  and the separated circularly shaped portions  85  of the insulator layer  83  are clearly apparent. 
         [0090]    Next, a semiconductor layer  90  is epitaxially grown from the exposed portions of the seed layer structure  82 , firstly mainly vertically and then onto each of the separated circularly shaped portions  85  of the insulator layer  83  until the epitaxially grown semiconductor layer  90  coalesces with each of the separated circularly shaped portions  85  of the insulator layer  83 . The epitaxial growth may be performed as disclosed above with reference to  FIG. 1 a   - g.    
         [0091]    The semiconductor structure  81  may be a silicon substrate, the seed layer structure  82  may consist of, or comprise as uppermost layer, a seed layer, formed by MOVPE as disclosed above. The insulator layer  83 , which may be an oxide or a nitride, may be formed thereon, e.g. by PECVD. The openings  84  in the insulator layer  83  may be formed by ordinary lithographic technology. 
         [0092]    Similar to previous embodiments, the epitaxially grown semiconductor layer forms a first region  90   a  having a first defect density during the mainly vertical growth and a second region  90   b  having a second defect density during the growth onto each of the separated circularly shaped portions of the insulator layer, wherein the second defect density is preferably lower than the first defect density. 
         [0093]    The second defect density may be lower than 10 8  cm −2 , preferably lower than 10 7  cm −2 , more preferably lower than, or in the order of, 10 6  cm −2 , whereas the first defect density may be higher than 10 8  cm −2 , and preferably higher than 10 7  cm −2 . The exposed at least portion of the seed layer structure has a third defect density, which may be in the same order of magnitude as the first defect density. 
         [0094]      FIG. 5  illustrates schematically a semiconductor device in a side sectional view with a heterostructure according to an embodiment preferably manufactured according to the disclosure with respect to  FIGS. 3 a   - f.    
         [0095]    The surface  50   a  of the semiconductor structure or substrate  50  exposed in the one or more circularly shaped openings  53 , is engineered to obtain a texture by chemical or dry etching or patterned by lithography and dry etching to nano-sized structures of circular, square, triangle or any other shape. Such texture may result in certain functionality in semiconductor structure or substrate  50  or may modify the properties of the semiconductor structure or substrate  50 , such as absorption coefficient or refractive index, etc. The texture can be made into the semiconductor structure or substrate  50  at a stage in the manufacturing process shown in  FIG. 3   b.    
         [0096]    The texture can be made to the semiconductor structure or substrate  50  in any of the other process flows as disclosed above. For instance, the texture can be made into the semiconductor structure or substrate  50  at a stage in the manufacturing process shown in  FIG. 1   e.    
         [0097]      FIGS. 6 a - b    illustrate schematically a semiconductor device with a heterostructure according to a further embodiment.  FIG. 6 a    is a side sectional view, whereas  FIG. 6 b    is a sectional view along line A-A of  FIG. 6   a.    
         [0098]    The semiconductor device is a multi pixel avalanche photo diode based detector, wherein the semiconductor structure or substrate  50  is an n-type doped silicon substrate with a plurality of p-type doped silicon pixel areas  701  thereon, the epitaxially grown semiconductor layer  80  is an In x Ga 1-x AsyP 1-y  absorption layer, and a p+-type doped In x ′, Ga 1-x ′As y ′P 1-y ′ light receiving layer  702  is formed thereon. 
         [0099]    The p-type doped silicon pixel areas  701  may be formed at the same phase in the process flows as the texture of  FIG. 5  is formed and they may be formed in the substrate, e.g. by means of etching the substrate, or by depositing an epitaxial layer, which is subsequently etched. The doping may be performed in any appropriate manner. 
         [0100]    The dimension of the p-type silicon pixel areas  701  can be reduced to some hundreds of nanometer, or less, and the distance between the pixels can be 100 nm to several micrometer. The composition of the In x Ga 1-x AsyP 1-y  absorption layer  80  can be tuned to have different band gaps for different wavelengths of the photons absorbed. 
         [0101]      FIGS. 7 a - b    illustrate schematically a semiconductor device with a heterostructure according to a yet further embodiment.  FIG. 7 a    is a side sectional view, whereas  FIG. 7 b    is a sectional view along line A-A of  FIG. 6   a.    
         [0102]    The semiconductor device is a single pixel avalanche photo diode based detector, wherein the semiconductor structure or substrate  50  is an n-type doped silicon substrate with a single p-type doped multiplication layer  701  thereon, the epitaxially grown semiconductor layer  80  is an InxGa 1-x AsyP 1-y  absorption layer, and a p+-type doped In x ′Ga 1-x ′As y ′P 1-y ′light receiving layer  702  is formed thereon. The single p-type doped multiplication layer  701  may be formed at the same phase in the process flows as the texture of  FIG. 5  is formed and it may be formed in the substrate or as a separately deposited epitaxial layer. 
         [0103]    The composition of the In x Ga 1-x AsyP 1-y  absorption layer  80  can be tuned to have different band gaps for different wavelengths of the photons absorbed. 
         [0104]    The semiconductor devices of  FIGS. 6 and 7  are examples of devices that can be manufactured according to any of the manufacturing methods disclosed with reference to  FIGS. 1-3 . It shall be appreciated that the epitaxially grown semiconductor layer  80  shown in  FIGS. 6 and 7  is a layer portion within a single one of the one ore more of the openings  53  ( FIGS. 1-3 ).