WO2022094283A1 - Selective-area mesoporous semiconductors and devices for optoelectronic and photonic applications - Google Patents

Abstract

At least one selective-area mesoporous semiconductor material is formed by one or more selective-area n-type doped structures with one or more different doping levels, wherein a porosity of the selective-area n-type doped structures is controlled by selective-area doping followed by electrochemical (EC) etching. Various geometries are disclosed for optics, optoelectronics, and photonics applications. The applications include optical gratings and optical filters, various geometry Tamm plasmon lasers, monolithic RGBY displays, lateral cavities, ring DBRs, meta materials, and photonic doping.

Description

SELECTIVE- AREA MESOPOROUS SEMICONDUCTORS AND DEVICES FOR OPTOELECTRONIC AND PHOTONIC APPLICATIONS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. Section 119(e) of the following co-pending and commonly-assigned application:

U.S. Provisional Application Serial No. 63/107,535, filed on October 30, 2020, by Guillaume Lheureux, Morteza Monavarian, Steven P. DenBaars and James S. Speck, entitled “SELECTIVE-AREA MESOPOROUS SEMICONDUCTORS AND DEVICES FOR OPTOELECTRONIC AND PHOTONIC APPLICATIONS,” attorneys’ docket number G&C 30794.0753USP2 (UC 2020-083-2); which application is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

This invention relates generally to selective-area mesoporous/nanoporous semiconductors and devices for optoelectronic and photonic applications.

2. Description of the Related Art.

(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets [x] . A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)

Nanoporous technology has recently gained a significant attention in the semiconductor community for applications in optoelectronics and photonics. [1-3] Due to the reduction of the semiconductor refractive index by introducing air-voids in mesoporous (also called “nanoporous”) material with respect to the bulk [4], the index contrast between the bulk and mesoporous layers may result in optical confinement. [5] To give an example, nanoporous distributed Bragg reflectors (DBRs) have been demonstrated for Ill-nitride systems, resulting in both optically [1,3] and electrically injected [2] lasers. Single nanoporous semiconductors have also been used for lateral mode confinement in edge-emitting lasers. [5] The nanoporous semiconductors can be implemented using electrochemical (EC) etching of an w-type doped semiconductor.

[6]

There is a need in the art for improved designs and methods of using selective- area mesoporous semiconductors and devices for optoelectronic and photonic applications. The present invention satisfies this need.

SUMMARY OF THE INVENTION

The present invention discloses various geometries for various selective-area mesoporous semiconductor architectures for optics, optoelectronics, and photonics applications. Applications include optical gratings and optical filters, various geometry Tamm plasmon optical sensors, confined and two dimensional Tamm plasmon lasers, monolithic red-green-blue-yellow (RGBY) displays, lateral cavities, ring DBRs, meta materials, and photonic doping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic representation of an electrochemical (EC) etching system, FIG. 1(b) is a schematic representation of a sample comprised of porous Si- doped GaN, and FIG. 1(c) is an enlarged view of the porous Si-doped GaN.

FIG. 2 is a graph of doping concentration (cm'³) vs. applied bias (V) providing a phase diagram for EC etching.

FIG. 3 is a simulated graph of reflectivity vs. wavelength (nm) illustrating the reflectivity of a nonporous GaN DBR and 45 nm Ag + GaN nonporous DBR.

FIG. 4(a) is a schematic representation of a Tamm plasmon structure with a nanoporous GaN DBR, and FIG. 4(b) is an enlarged view of the nanoporous GaN DBR. FIG. 5 is a density map of reflectivity as a function of wavelength and porosity of the low-index X/4 layer for a DBR with 16 pairs.

FIG. 6 is a simulated graph of reflectivity vs. wavelength that shows a simulation of a Tamm plasmon structure with nanoporous GaN with different refractive index of the nanoporous layer as a result of an exposure to different materials filling the pores.

FIG. 7 is a density map of reflectivity as a function of wavelength and an optical refractive index of the porous material («_pOr) for a simulation of the reflectivity of a Tamm plasmon structure with nanoporous GaN with different refractive indices corresponding to the pores being filled with different materials.

FIG. 8 shows a simplified possible geometry for an integrated Tamm Plasmon sensor with a nanoporous GaN DBR that utilizes a light emitter and a detector.

FIGS. 9(a), 9(b), 9(c) and 9(d) show examples of optical gratings and metamaterials fabricated using this invention. FIGS. 9(a) and 9(b) corresponds to mesoporous/nanoporous structures and FIGS. 9(c) and 9(d) corresponds to air gap structures.

FIGS. 10(a), 10(b), 10(c) and 10(d) show an all-around DBR which surrounds a cavity. FIGS. 10(a) and 10(b) corresponds to mesoporous/nanoporous structures and FIGS. 10(c) and 10(d) corresponds to air gap structures.

FIG. 11 is a cross-sectional schematic of a three dimensional cavity using selective-area mesoporous (or air-gap) semiconductor lateral DBRs, and top and bottom DBRs.

FIG. 12(a) is a plane-view schematic of arrays of four different mesa structures, including non-porous, low, medium, and high porosity GaN.

FIG. 12(b) is a plane-view schematic of the structure of FIG. 12(a) after growth of an InGaN active region on top resulting in multi-color emission lightemitting diodes for RGBY displays.

FIGS. 13(a) and 13(b) are cross-sectional schematics of a semiconductor structure after dry etching a trench and EC electropolishing, respectively. FIGS. 14(a), 14(b), 14(c), 14(d), 14(e) and 14(f) are schematics that illustrate a Si or Ge solid-state diffusion process flow.

FIGS. 15(a), 15(b), 15(c), 15(d), 15(e) and 15(f) are schematics that illustrate a process flow for a selective-area nanoporous/mesoporous or air gap GaN formation using a Si or Ge solid-state diffusion process.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

Technical Description

The present invention discloses various geometries for various selective-area mesoporous semiconductor architectures for optics, optoelectronics, and photonics applications using Ill-nitrides. For example, in the case of GaN, Si-doped layers can be grown by metal-organic chemical vapor deposition (MOCVD) followed by EC etching.

FIG. 1(a) is a schematic representation of an EC etching system 100, according to one embodiment. A vessel 101 that has a stir bar 102 is filled with an etchant 103. A sample 104 with an Indium contact 105 is an anode and a platinum (Pt) mesh 106 is a cathode. The anode 104 and cathode 106 are coupled to a DC power supply 107 that includes an Amp meter 108, and then the anode 104 and cathode 106 are immersed in the etchant 103 contained in the vessel 101. When power is applied by the DC power supply 107, and the etchant 103 is stirred by the stir bar 102, the sample 104 is porosofied.

FIG. 1(b) is a schematic representation of the sample 104, which is comprised of a GaN/Sapphire substrate 109, unintentionally-doped (UID) GaN 110 deposited on the GaN/Sapphire substrate 109, Si-doped GaN 111 deposited on the UID GaN 110, and the Indium contact 105 deposited on the Si-doped GaN 111.

FIG. 1(c) is an enlarged view of the porous Si-doped GaN 103 after the EC etching by system 100.

In this method, the porosity of nanoporous GaN can be controlled by doping levels and EC conditions, i.e. bias voltage and solution. Most of the demonstrated nanoporous technologies have been on planar structures due to the ease of implementation particularly in terms of MOCVD growth and doping.

In this invention, various planar and selective-area mesoporous semiconductor architectures for optics, optoelectronics, and photonics applications are proposed. Structures considered include optical sensors on Tamm plasmon resonance, vertical emitting lasers and ridge emitting lasers based on confined and unconfined Tamm plasmon resonance, optical gratings, monolithic RGBY displays, lateral cavities, ring DBRs, metamaterials, and photonic doping. The invention can also provide a path toward damage-free selective-area etching or as a method to remove the dry etch- induced damage in various electronic and optoelectronic applications.

The invention comprises selective-area doping followed by controlled EC etching. Various pattern shapes, orientations can be considered. In all the applications, different porosity of the mesoporous semiconductor is considered, which can be controlled by doping levels and EC etching conditions, such as bias voltage, solution type and molarity. In extreme EC conditions, electropolishing (100% porosity) can also be obtained, which is beneficial for damage-free selective-area semiconductor etching.

FIG. 2 shows various types of porosity which could be obtained by EC etching under different bias voltages and/or doping levels. [6] Specifically, FIG. 2 is a graph of doping concentration (cm'³) vs. applied bias (V) illustrating a processing phase diagram for EC etching, wherein a first dashed line encircles the mesoporous region for photonic applications, and a second dashed line encompasses the macroporous region for light-scattering applications. A possible direct application of the selective-area or planar nanoporous GaN technology could be an optical sensor based on the sensitivity of the Tamm plasmon resonance on refractive indices of the stacks of the DBR. Tamm plasmons are electromagnetic defect states that can be formed at the interface of a thin-film metallic layer and a DBR.

FIG. 3 is a graph of reflectivity vs. wavelength (nm) illustrating the simulated reflectivity of a nanoporous DBR and 45 nm Ag + DBR. Their energy features an inplane wave vector parabolic dispersion relation lying inside the DBR stop-band and within the light cone so that these modes can be optically directly accessed at normal incidence. Moreover, the Tamm resonance electric field is confined at the metal-DBR interface, and, since the field penetration inside the DBR is about 2 orders of magnitude larger than that in the metal layer, they present reduced losses compared to surface plasmons. The properties of the mode can be controlled by engineering the top layer. [7,8] One interesting feature is that they can be coupled to surface plasmons. [12] As a surface state, the Tamm plasmon is extremely sensitive to the environment.

The idea is to use a Tamm plasmon structure as a sensor where the DBR is a nanoporous GaN DBR. FIG. 4(a) illustrates a Tamm plasmon structure 400 comprised of a nanoporous GaN DBR 401 and metal nano-layer 402. The DBR 401 is made of alternating high-index and low-index layers, as shown in the enlarged view of FIG. 4(b), comprised of a X/4n nanoporous GaN layer 403 and a X/4n GaN layer 404, respectively. The thickness of the layers 403, 404 are precisely determined by the central position of the stopband and the optical index of the layers 403, 404. Contrary to more conventional DBRs, the different layers 403, 404 are made of the same material (GaN). As shown in FIG. 2(a) from reference [6], the optical index of the low index layers 403 are controlled by changing the porosity of the layers 403, as described below. The thickness of the metallic layer 402 is also critical for the properties of the mode and can be easily tuned. The choice of the metal allows also for an additional degree of freedom to match the needs at different wavelength. This type of DBR 401 allows precise control of the stopband of the DBR by changing the porosity. This type of DBR 401 has been recently used to achieve a vertical emitting laser. [14] To the best of the inventors’ knowledge, a Tamm plasmon structure 400 with a GaN DBR 401 has never been reported in the literature. The closest demonstration was a Tamm plasmon structure with a dielectric mesoporous DBR. [9] The authors demonstrated the feasibility of a sensor based on Tamm Plasmon structures. There is also a patent on the Tamm plasmon structure for sensing. [10]

FIG. 5 is a density map of reflectivity as a function of wavelength (nm) and porosity (%) of the low-index X/4 layer for a DBR with 16 pairs. The pores are assumed to be filled with air (flair =1). The Tamm plasmon mode is the depth in reflectivity. As the porosity changes, the Tamm plasmon shifts to a lower wavelength, allowing for some tunability.

The Tamm plasmon is also very sensitive to the material that fills the pores of the nanoporous DBR. FIG. 6 is a graph of reflectivity vs. wavelength (nm) that shows a simulation of a Tamm plasmon structure with nanoporous GaN with different materials in the pores at a normal incidence. Specifically, FIG. 6 shows the reflectivity of Tamm plasmon structure with a 45 nm Ag 16 pairs DBR and a fixed porosity (53%) for different materials in the pores (each with a different optical refractive index A). The shift of the resonance shows that the Tamm mode can be used as a sensor.

A small change in the optical refractive index leads to a shift of the resonance to a longer wavelength. This shift can be used as a way to track the presence of a gas or a liquid different from the air. Additional simulations will be needed to study the way to improve sensitivity. Currently, the simulated sensitivity of such devices, defined as n/ k, is on the order of 0.1 nm'¹.

FIG. 7 is a density map of reflectivity as a function of wavelength (nm) and an optical refractive index of the material in the pores (flpor) for a simulation of the reflectivity of a Tamm plasmon structure with nanoporous GaN with different materials in the pores at a normal incidence. Specifically, FIG. 7 shows the variation of the Tamm plasmon mode as the refractive index of the material in the pores is continuously increased. The shift of the resonance shows that the Tamm mode can be used as a sensor.

FIG. 8 is a schematic representation that shows a simplified possible geometry for an integrated Tamm plasmon sensor 800 with a nanoporous GaN DBR 801 and metal nano-layer 802 that uses a light emitter 803 and detector 804. Different configurations can be considered depending on the geometry of the nanoporous GaN DBR 801 and the application. The light detector 804 may comprise an optical sensor that can be applied for sensing various substances, such as Alcohol, Hydrogen, CO2, CO, Methane, etc., for different applications. Moreover, different DBR configurations can be considered, such as periodic and random DBRs (a random DBR refers to the DBR stacks with at least one of the stack thicknesses are randomly varied around an average thickness). In this invention, various geometries are considered for the Tamm plasmon resonance sensors and emitters, including planar DBRs and bottom-up planar or core-shell DBRs. The conformal deposition of the top metal can lead to large area lasing in different directions.

It is believed that the Tamm plasmon sensor with nanoporous GaN presents several original concepts compared to similar inventions and demonstrations [9,10] from the literature. The original concepts include use of nanoporous GaN, both passive and active structures, and the fact that semiconductor active regions can be grown in the structures (easier to incorporate with semiconductor than dielectric systems). Also, the technique used to make the nanoporous GaN allows for the creation of air gap DBRs or random DBRs resulting in a very wide stop-bands. In addition, as demonstrated in FIG. 2(a) from reference [6], the porosity can be controlled in a very repeatable way, thus making the mode very tunable. Finally, the use of a semiconductor structure grown by MOCVD allows for fast industrial deployment. Other applications for selective-area porosmcation include optical gratings, metamaterials, and photonic doping. [11,12] FIGS. 9(a), 9(b), 9(c) and 9(d) show examples of optical gratings and metamaterial designs fabricated using the method described in this invention, and wherein FIGS. 9(a) and 9(b) are cross-sectional (top) and plane-view (bottom) schematics, respectively, of an example of UID semiconductor 900 with selective-area nanoporous ring gratings 901 for optical gratings and metamaterials, and FIGS. 9(c) and 9(d) are cross-sectional (top) and plane-view (bottom) schematics, respectively, of an example of UID semiconductor 900 with air-gap ring gratings 902 for optical gratings and metamaterials.

The shape of the gratings is arbitrary, and various shapes and geometries can be considered. Porosity, shape, depth of the features, and pitch size (separation between the features), are engineering parameters. Depending on the size of the features, optical gratings for different interaction wavelengths can be considered. Even air-gap structures (100% porosity) can be considered by controlling the EC etching conditions. The light-matter interaction can be engineered by controlling the design configurations.

Similar structures to those shown in FIGS. 9(a), 9(b), 9(c) and 9(d) can be considered for lateral optical confinement of lasers. In addition, lateral DBRs can be fabricated using similar methods. FIGS. 10(a), 10(b), 10(c) and 10(d) show an all- around DBR which surrounds a cavity, wherein FIGS. 10(a) and 10(b) are cross- sectional (top) and plane-view (bottom) schematics, respectively, of an example of UID semiconductor 1000 with selective-area mesoporous lateral DBR ring gratings 1001 that surround a cavity 1002 for lateral confinement and lasing, and FIGS. 10(c) and 10(d) are cross-sectional (top) and plane-view (bottom) schematics, respectively, of an example of UID semiconductor 1000 with air-gap lateral ring gratings 1003 that surround a cavity 1002 for optical gratings and metamaterials.

These structures 1001, 1003 provide a significantly higher lateral optical confinement, which can reduce the lasing threshold and improve lasing output power for vertical-cavity surface-emitting lasers (VCSELs). A ridge laser or an edge- emitting laser or a laser diode (LD) can also incorporate such lateral DBRs 1001, 1003 instead of a cleaved facet mirror to reduce the lasing threshold and enhance the output power. Even air-gap lateral DBRs 1003 (100% porosity) can be considered by controlling the EC etching conditions. The thickness of the DBR stacks (depending on the target wavelengths), number of pairs, vertical depth, and porosity, are engineering parameters. Different planar shapes of the DBRs, such as rectangles, triangles, rings, etc., can be considered.

Also, the lateral DBRs can be used along with a bottom and a top DBR (either semiconductor, dielectric, or nanoporous semiconductor) to make a fully three dimensional cavity. FIG. 11 is a cross-sectional schematic of a three dimensional cavity 1100 using selective-area mesoporous (or air-gap) semiconductor lateral DBRs 1101, and top and bottom DBRs 1102, 1103. The top or bottom DBRs 1102, 1103 can be either semiconductor, or dielectric, or nanoporous semiconductor DBRs.

Another area where the selective-area mesoporous semiconductor can be used is monolithic multi-color integration of RGBY displays. The porosity of the GaN buffer layer and the resulting strain has shown to have a significant impact on the emission color of the overgrown active regions. [13] Also, the thermal conductivity of the nanoporous GaN is strongly dependent on its porosity. Therefore, temperature sensitive growths such as an InGaN active region are dependent on the porosity of the buffer layer. Hence, by controlling the porosity of the mesoporous GaN buffer layer (by controlling the doping and/or EC etching conditions), different emission colors can be obtained. Thus, if various porosity is provided on different mesa structures on the same chip (this can be done by separate EC etching of selected mesas while others are entirely protected by dielectric mask layers), after growth of a calibrated active region, multi-color emissions can be obtained monolithically on a single chip.

FIGS. 12(a) and 12(b) are plane view schematic of arrays of UID semiconductor 1200 with four different mesa structures 1201, including not porous, as well as low, medium, and high porosity, before (as shown in FIG. 12(a)), and after (as shown in FIG. 12(b)), growth of LED structures 1202 on a single chip. The colors emitted by the LED structures 1202 in FIG. 12(b) are represented by R (red), G (green), B (blue) and Y (yellow), and schematically show that LED structures 1202 with different emission colors can be monolithically integrated on the same chip, thanks to the selective-area mesoporous method described in this invention.

Such monolithically -integrated multi-color LEDs (large-area LEDs or micro LEDs) can be used in multi-color micro-pixel display technologies for regular displays as well as near-to-eye displays in virtual reality (VR) and augmented reality (AR). Porosities, shape and thicknesses of the mesas, configurations of the arrays, and growth conditions on the prepared mesa templates, are engineering parameters for this application. The proposed design for monolithic RGBY LEDs for high-resolution displays, can overcome numerous challenges with conventional micro-LEDs for display, including color variations with temperature due to the use of different III-V materials to make the three primary colors (RGB) and the need for difficult pick-and- place manufacturing technologies.

FIGS. 13(a) and 13(b) are cross-sectional schematics of a semiconductor structure comprised of a substrate 1300 and UID semiconductor 1301 after dry etching of a trench 1302 as shown in FIG. 13(a), and EC electropolishing as shown in FIG. 13(b). The selective-area EC etching can be used to remove dry-etch induced damage 1303, as shown in FIG. 13(a), by conventional etching tools such as inductively coupled plasma (ICP) or reactive ion etching (RIE). If not treated, the damage 1303 and impurities 1304 caused by dry etching can have significant adverse effects on the final semiconductor device. Under extreme bias voltage and doping concentrations in EC etching, the structure can experience electropolishing which can be used to remove, as shown in FIG. 13(b), damage 1303 and impurities 1304 generated by dry etching. The EC etching can also be used as a standalone damage- free etching tool in the semiconductor processing industry. EC etching conditions (such as doping, bias voltage, etching time, solution type and molarity), pattern shapes, sizes, and configurations, are key engineering parameters. The EC etching standalone tool can also be used for manufacturing micro-LEDs for display and visible-light communication where the sidewall damage induced by conventional etching tools reduces the LED efficiency.

The selective-area doping required for this invention can be performed by either (i) selective-area epitaxy by MOCVD, molecular-beam epitaxy (MBE) or any other epitaxy method, or (ii) selective-area Ga to Ge neutron transmutation doping, or (iii) selective-area Si or Ge solid-state diffusion. For any of the methods, standard photolithography for regular sized features and interferometric lithography and nanoimprint for smaller features can be considered.

For epitaxy, a bottom-up approach for either planar or core-shell nanoporous designs can be considered. The core-shell nanostructure-based nanoporous semiconductor can use MOCVD or MBE on patterned substrates. Selective-area epitaxy can be performed using dielectric or metal hard masks.

The selective-area doping can also be considered using transmutation doping approaches. Neutron transmutation of Ga to Ge by interaction of the neutron transmutation doping of GaN to fabricate uniform heavily doped w-type GaN wafers. The neutron transmutation doping process, which consists of exposing GaN wafers to neutron radiation to create a stable network of the dopant Ge within the GaN wafer, results in high level uniform doping concentrations across the wafer. Selective-area doping using transmutation can be done by masking (with materials such as Pb) regions of the wafer while keeping other regions exposed to irradiation and thus n- type doping.

Selective-area diffusion is a process which relies on an exchange of Si to Ga in the GaN crystal via solid-state diffusion. FIGS. 14(a), 14(b), 14(c), 14(d), 14(e) and 14(f) are schematics that illustrate an Si or Ge diffusion process flow, wherein FIG. 14(a) shows a substrate 1400 comprising a GaN / Sapphire, Si, SiC or freestanding GaN substrate 1400, and UID or lightly doped GaN 1401 growth on or above the substrate 1400; FIG. 14(b) shows deposition of a layer 1402 comprised of Si or Ge or their compound, and Pd or Pt 1403; FIGS. 14(c) and 14(d) show Si or Ge diffusion 1404 and Gallide formation 1405 at elevated temperatures (800 °C to 1000 °C); FIG. 14(e) shows the resulting n-GaN layer 1406 and Galhde layer 1407; and FIG. 14(f) shows removal of the Pd or Pt 1403 and Gallide layer 1406 from the surface. As noted in this process flow, an Si or Ge layer (or their compounds) 1402 followed by a Pd or Pt layer 1403 is deposited on UID or lightly doped GaN 1401 on the substrate 1400. Upon elevating temperature (800 °C to 1000 °C), the Si or Ge atoms 1404 start to diffuse to the UID or lightly doped GaN 1401, while Ga atoms 1404 migrate out of the surface toward the metallic layer 1403 and start to form a Galhde layer 1405 at the semiconductor-metal interface. Si or Ge atoms replace Ga in the crystal and serve as shallow donors. Without the need for another crystal epitaxy step, a layer of w-type GaN 1407 can therefore be obtained after removing the metal layer 1403 and the formed Galhde layer 1405.

FIGS. 15(a), 15(b), 15(c), 15(d), 15(e) and 15(f) are schematics that illustrate a process flow for a selective-area nanoporous GaN formation using Si or Ge solid-state diffusion process, wherein FIG. 15(a) shows a substrate 1500 and UID or lightly doped GaN 1501 growth on the substrate 1500; FIG. 15(b) shows selective-area deposition of a layer 1502 of Si or Ge or their compounds, and Pd or Pt 1503; FIG. 15(c) shows selective-area Si or Ge diffusion 1504 and Galhde formation 1505 at elevated temperatures (800 °C to 1000 °C); FIG. 15(d) shows removal of the metal 1503 and Galhde 1505 from the surface; FIG. 15(e) shows EC etching and selective- area mesoporous GaN 1506 formation; and FIG. 15(f) shows a top view of the final processed structure with the selective-area mesoporous GaN 1506.

The shapes and configurations of the features, type of dopant (Si or Ge), doping levels, diffusion annealing temperature, and porosity, which is controlled by doping conditions and EC etching conditions, can all be engineered for various applications. Similar methods can be applied to other different semiconductors, such as GaAs, InP, etc., for different wavelengths. Process Steps

FIG. 16 is a flowchart that describes a method for fabricating an embodiment of the present invention.

Block 1600 represents the step of providing a substrate, wherein the substrate has a Ga-polar c-plane, N-polar c-plane, nonpolar or semipolar orientation.

Block 1601 represents the step of forming a semiconductor material on a substrate. In one embodiment, the semiconductor material is a Ill-nitride material.

Block 1602 represents the step of forming at least one selective-area mesoporous semiconductor material using one or more selective-area w-type doped structures with one or more different doping levels, wherein a porosity of the selective-area w-type doped structures is controlled by selective-area doping followed by electrochemical (EC) etching.

In one embodiment, the selective-area doping is performed by selective-area epitaxy.

In various embodiments, the selective-area epitaxy comprises metal-organic chemical vapor deposition or molecular-beam epitaxy.

In another embodiment, the selective-area epitaxy is performed by a neutron transmutation doping process that comprises a neutron transmutation reaction of Ga to Ge. In one embodiment, the selective-area doping uses mask layers such as Pb after the neutron transmutation doping process.

In another embodiment, the selective-area doping is performed by Si or Ge solid-state diffusion.

In various embodiments, the electrochemical etching uses different electrochemical etching solutions and molarities, and different bias voltages.

In various embodiments, the selective-area mesoporous semiconductor material is used for lateral or vertical optical confinement in any light emitting applications.

In various embodiments, the selective-area w-type doped structures have a rectangular, triangular, circular or ring geometry. In various embodiments, the selective-area w-type doped structures are comprised of one or more patterns; the patterns comprise circles or stripes with different openings, pitch sizes, or orientations; and the patterns have the same or different porosities on the same chip.

In various embodiments, the selective-area /7-type doped structures include a lateral or vertical distributed Bragg reflector (DBR), and the DBR is an air-gap DBR with 100% porosity or the DBR is comprised of random layer thicknesses that allows for emergence of a photonic stop band.

In various embodiments, various configurations of the selective-area mesoporous semiconductor material are used for optical filters, optical gratings, metamaterials or any other applications involving engineered light-matter interaction.

Block 1603 represents the step of monolithically growing one or more active regions on the patterns.

In various embodiments, the active regions are monolithically grown on the patterns with different porosities, and the active regions emit at different wavelengths.

Block 1604 represents the step of annealing the selective-area /7-type doped structures, wherein different annealing temperatures are used to obtain different depths of /7-type material in the selective-area w-type doped structures.

Block 1605 represents the step of depositing a metal on top of a high index layer of a DBR obtained through the selective-area w-type doped structures to give rise to Tamm Plasmon modes. Consequently, a result device may be a passive Tamm Plasmon structure, a Tamm Plasmon sensor, a confined Tamm state structure, an electrically injected Tamm Plasmon laser ridge emitting laser, an electrically injected Tamm Plasmon vertical emitting laser, or an electrically injected Tamm Plasmon emitting diode.

Block 1606 represents the final result, namely, a device comprising at least one selective-area mesoporous semiconductor material formed by one or more selective-area /7-type doped structures with one or more different doping levels, wherein a porosity of the selective-area w-type doped structures is controlled by selective-area doping followed by electrochemical (EC) etching.

Benefits and Advantages

The benefits and advantages of this invention include:

(i) enhanced optical confinement and reduce lasing threshold in lasers,

(ii) high-sensitivity optical sensors by Tamm plasmon resonance on nanoporous DBRs,

(iii) design flexibility of passive optical elements such as optical gratings, metamaterials, and photonic doping,

(iii)viable approach toward photonic integrated circuits by lateral passive and active elements,

(iv) ease of implementation by industrially viable MOCVD growth approach,

(v) high-quality lattice-matched index contrast layers and DBRs,

(vi) monolithic RGBY LED displays,

(vii) method of dry-etch induced damage removal and providing a damage- free standalone etching tool, and

(viii) electric sensor easily compatible with industry processes.

This method can be applied to any crystal orientation of nitrides, polar (either Ga-face or N-face), nonpolar and semipolar planes. The method can be applied to other material systems for optical elements emitting in different wavelengths.

References

The following publications are incorporated by reference herein:

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[14] G. Lheureux, M. Monavarian, R. Anderson, A. Decrescent, J. Bellessa, C. Symonds, J. A. Schuller, J.S. Speck, S. Nakamura and S.P. DenBaars, "Tamm plasmons in metal/nanoporous GaN distributed Bragg reflector cavities for active and passive optoelectronics," Optics Express, Vol. 28, No. 12, pp. 17934-17943 (8 June 2020). Nomenclature

The terms “Group-Ill nitride” or “Ill-nitride” or “nitride” or “III-N” as used herein refer to any composition or material related to (B, Al, Ga, In)N semiconductors having the formula BwAlxGa_yIn_zN where 0 < w < 1, 0 < x < 1, 0 < y < 1, 0 < z < 1, and w + x + y + z = l. These terms as used herein are intended to be broadly construed to include respective nitrides of the single species, B, Al, Ga, and In, as well as binary, ternary and quaternary compositions of such Group III metal species. Accordingly, these terms include, but are not limited to, the compounds of AIN, GaN, InN, AlGaN, AllnN, InGaN, and AlGalnN. When two or more of the (B, Al, Ga, In)N component species are present, all possible compositions, including stoichiometric proportions as well as off-stoichiometric proportions (with respect to the relative mole fractions present of each of the (B, Al, Ga, In)N component species that are present in the composition), can be employed within the broad scope of this invention. Further, compositions and materials within the scope of the invention may further include quantities of dopants and/or other impurity materials and/or other inclusional materials.

This invention also covers the selection of particular crystal orientations, directions, terminations and polarities of Ill-nitride materials. When identifying crystal orientations, directions, terminations and polarities using Miller indices, the use of braces, { }, denotes a set of symmetry-equivalent planes, which are represented by the use of parentheses, ( ). The use of brackets, [ ], denotes a direction, while the use of brackets, < >, denotes a set of symmetry-equivalent directions.

Many III -nitride devices are grown along a polar orientation, namely a c-plane {0001} of the crystal, although this results in an undesirable quantum-confined Stark effect (QCSE), due to the existence of strong piezoelectric and spontaneous polarizations. One approach to decreasing polarization effects in Ill-nitride devices is to grow the devices along nonpolar or semipolar orientations of the crystal.

The term “nonpolar” includes the {11-20} planes, known collectively as a- planes, and the {10-10} planes, known collectively as m-planes. Such planes contain equal numbers of Group-Ill and Nitrogen atoms per plane and are charge-neutral. Subsequent nonpolar layers are equivalent to one another, so the bulk crystal will not be polarized along the growth direction.

The term “semipolar” can be used to refer to any plane that cannot be classified as c-plane, a-plane, or m-plane. In crystallographic terms, a semipolar plane would be any plane that has at least two nonzero h, i, or k Miller indices and a nonzero 1 Miller index. Subsequent semipolar layers are equivalent to one another, so the crystal will have reduced polarization along the growth direction.

A “microporous” material is a material having pores with diameters smaller than 2 nm, a “mesoporous” material is a material having pores with diameters between 2 and 50 nm, and a “macroporous” material is a material having pores with diameters larger than 50 nm. A “nanoporous” material is a material having pores with diameters generally 100 nm or smaller.

Conclusion

This concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more 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. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A device, comprising: at least one selective-area mesoporous semiconductor material formed by one or more selective-area w-ty pe doped structures with one or more different doping levels, wherein a porosity of the selective-area w-ty pe doped structures is controlled by selective-area doping followed by electrochemical (EC) etching.

2. The device of claim 1, wherein the semiconductor material is a III- nitride material.

3. The device of claim 2, wherein the semiconductor material is formed on a substrate, and the substrate has a Ga-polar c-plane, N-polar c-plane, nonpolar or semipolar orientation.

4. The device of claim 1, wherein the selective-area w-type doped structures have a rectangular, triangular, circular or ring geometry.

5. The method of claim 4, wherein the selective-area mesoporous semiconductor material is used for lateral or vertical optical confinement in any light emitting applications.

6. The device of claim 1, wherein the selective-area w-type doped structures are comprised of one or more patterns, and the patterns comprise circles or stripes with different openings, pitch sizes, or orientations.

7. The method of claim 6, wherein various configurations of the selective-area mesoporous semiconductor material is used for optical filters, optical gratings, metamaterials or any other applications involving engineered light-matter interaction.

8. The device of claim 6, wherein the patterns have the same or different porosities on the same chip.

9. The device of claim 8, wherein one or more active regions are monolithically grown on the patterns with the different porosities for monolithic RGBY displays.

10. The device of claim 9, wherein the active regions emit at different wavelengths.

11. The device of claim 1, wherein the selective-area w-type doped structures include a lateral or vertical distributed Bragg reflector (DBR), and the DBR is an air-gap DBR with 100% porosity or the DBR is comprised of random layer thicknesses that allows for emergence of a photonic stop band.

12. The device of claim 11, wherein a metal is deposited on top of a high index layer of the DBR obtained through the selective-area w-ty pe doped structures to give rise to Tamm Plasmon modes.

13. The device of claim 12, where the device is a passive Tamm Plasmon structure, a Tamm Plasmon sensor, a confined Tamm state structure, an electrically injected Tamm Plasmon laser ridge emitting laser, an electrically injected Tamm Plasmon vertical emitting laser, or an electrically injected Tamm Plasmon emitting diode.

14. A method, comprising: forming at least one selective-area mesoporous semiconductor material using one or more selective-area w-type doped structures with one or more different doping levels, wherein a porosity of the selective-area w-ty pe doped structures is controlled by selective-area doping followed by electrochemical (EC) etching.

15. The method of claim 14, wherein the selective-area doping is performed by selective-area epitaxy.

16. The method of claim 14, wherein the selective-area epitaxy comprises metal-organic chemical vapor deposition or molecular-beam epitaxy.

17. The method of claim 14, wherein the selective-area epitaxy is performed by a neutron transmutation doping process that comprises a neutron transmutation reaction of Ga to Ge.

18. The method of claim 14, wherein the selective-area doping uses mask layers such as Pb after a neutron transmutation doping process.

19. The method of claim 14, wherein the selective-area doping is performed by Si or Ge solid-state diffusion.

20. The method of claim 14, wherein the electrochemical etching uses different electrochemical etching solutions and molarities.

21. The method of claim 14, wherein the electrochemical etching uses different bias voltages.

22. The method of claim 14, further comprising annealing the selective- area w-type doped structures, wherein different annealing temperatures are used to obtain different depths of w-type material in the selective-area w-type doped structures.