CN111668351B

CN111668351B - Heterostructure and light emitting device employing the same

Info

Publication number: CN111668351B
Application number: CN202010087849.2A
Authority: CN
Inventors: 张剑平; 高英; 周瓴
Original assignee: Bolb Inc
Current assignee: Bolb Inc
Priority date: 2019-03-06
Filing date: 2020-02-12
Publication date: 2023-05-12
Anticipated expiration: 2040-02-12
Also published as: CN113707773B; CN113707775A; CN113707774A; CN113707773A; CN113707774B; CN113707775B; CN111668351A

Abstract

Heterostructures are provided that contain one or more thin layers of positive charges or contain alternating stacks of AlGaN barriers and AlGaN potential wells having a specific thickness. Multiple quantum well structures and p-type contacts are also provided. The heterostructures, multiple quantum well structures and p-type contacts are useful in light emitting devices and photodetectors.

Description

Heterostructure and light emitting device employing the same

Technical Field

The present disclosure relates generally to semiconductor light emitting technology, and more particularly to heterostructures for light emitting devices or photodetectors, and to light emitting devices and photodetectors having heterostructures.

Background

Nitride semiconductors such as InN, gaN, alN and their ternary and quaternary alloys depending on the alloy composition, can achieve Ultraviolet (UV) radiation from 410nm to about 200 nm. These include UVA (400-315 nm) radiation, UVB (315-280 nm) radiation and partial UVC (280-200 nm) radiation. UVA radiation initiates a revolution in the curing industry, and UVB and UVC radiation are expected to find widespread use in the food, water and surface disinfection industries due to their bactericidal effects. UV light emitters made of nitride have inherent advantages over conventional UV light sources such as mercury lamps. In general, nitride UV emitters are robust, compact, spectrally tunable, and environmentally friendly. Which provides high UV light intensity to facilitate the desired disinfection/sterilization of water, air, food products and object surfaces. Further, the light output of the nitride UV light emitters can be intensity modulated at high frequencies up to several hundred megahertz, thereby ensuring their ability to serve as innovative light sources for internet of things, covert communication, and biochemical detection.

Existing UVC Light Emitting Diodes (LEDs) typically employ a laminate structure comprising c-plane sapphire or AlN as the UV transparent substrate, an AlN layer coated on the substrate that serves as an epitaxial template, and a set of AlN/AlGaN superlattices for dislocation and strain management. The AlN/AlGaN superlattice and/or AlN template enable growth of a high quality, highly conductive n-type AlGaN structure as an electron supply layer for injecting electrons into a subsequent AlGaN-based Multiple Quantum Well (MQW) active region. On the other side of the MQW active region is a p-type AlGaN structure comprising a p-type AlGaN layer for electron blocking, hole injection, hole supply and p-type ohmic contact formation. Conventional AlGaN UV LED structures can be found in the references (e.g., "Milliwatt power deep ultraviolet light-emitting diodes over sapphire with emission at 278nm", j.p. zhang, et al, APPLIED PHYSICS LETTERS 81,4910 (2002), the contents of which are incorporated herein by reference in their entirety).

As can be seen, UVC LEDs can utilize many AlGaN layers with different Al compositions to form an AlGaN heterostructure in order to achieve certain functionalities. The most important functionality is conductivity, which becomes more and more challenging for Al-rich AlGaN materials, because the activation energy of the donor and acceptor increases with increasing Al composition, resulting in a lack of free electron and hole carriers. Semiconductor superlattices are special types of semiconductor heterostructures made by periodically alternating stacks of at least two semiconductors with different bandgaps and taking advantage of the conduction and valence band edge discontinuities, which can enhance dopant activation to improve conductivity (see, e.g., "Enhancement of deep acceptor activation in semiconductors by superlattice doping", E.F.Schubert, W.Grieshaber and I.D.Goepfert, appl.Phys.Lett.69,9 (1996)). P-type Al has been proposed _x Ga _1-x N/Al _y Ga _1-y The N-superlattice replaces the conventional p-type AlGaN layer to improve conductivity (e.g., U.S. patent nos. 5,831,277, 6,104,039, and 8,426,225, the contents of which are incorporated herein by reference in their entirety).

The design rules for AlGaN heterostructures with improved conductivity and quantum confinement with respect to dopant concentration and interface charge density are disclosed.

Disclosure of Invention

A first aspect of the present invention provides a heterostructure for a light emitting device or photodetector comprising one or more p-type doped AlGaN layers, each of the one or more p-type doped AlGaN layers comprising one or more positively charged thin layers interposed therebetween, wherein the distance between two adjacent positively charged thin layers is greater than the depletion depth of a depletion region generated by either of the two adjacent positively charged thin layers.

Alternatively, the depletion depth of the depletion region generated by any one of the one or more thin layers of positive charge is less than 10nm.

The one or more positively charged thin layers may be formed by Si delta doping with a thin layer doping density of 1 x 10 ¹¹ –1×10 ¹³ cm ^-2 。

The p-doped AlGaN layer, which is placed closest to the active region of the light emitting device or photodetector, may contain more thin layers of positive charge, a higher Al composition and a greater thickness than the remaining layers of the one or more p-doped AlGaN layers.

The heterostructure may further include: a plurality of p-type doped AlGaN layers having no thin layers of positive charges therein, alternately stacked with said one or more p-type doped AlGaN layers having one or more thin layers of positive charges; wherein the Al composition of each of the plurality of p-type doped AlGaN layers that do not include a thin layer of positive charge is higher than the Al composition of an adjacent p-type doped AlGaN layer that includes one or more thin layers of positive charge, or the Al composition of each of the plurality of p-type doped AlGaN layers that do not include a thin layer of positive charge is lower than the Al composition of an adjacent p-type doped AlGaN layer that includes one or more thin layers of positive charge.

Optionally, the thin layer of positive charge divides each of the one or more p-doped AlGaN layers comprising the thin layer of positive charge into a thinner front region (priority zone) and a thicker back region (post zone).

The heterostructure may further include another p-type doped AlGaN layer on which the one or more p-type doped AlGaN layers are formed, wherein an Al composition of the other p-type doped AlGaN layer is in a range of 0.6 to 0.8 and a thickness is in a range of 1.0 to 5.0 nm.

A second aspect of the present invention provides a heterostructure for a light emitting device or photodetector comprising alternately stacked p-type doped AlGaN barriers and p-type doped AlGaN potential wells, wherein the thickness of each of the AlGaN barriers and AlGaN potential wells respectively satisfies:

Wherein h is _i Is the thickness of the ith AlGaN barrier or potential well; sigma (sigma) _i Is the sheet charge density of the charge sheet on the surface of the ith AlGaN barrier or well that is oppositely charged relative to the net active dopant in the ith AlGaN barrier or well; ρ is _0i ＝eN _Di -eN _Ai Is the maximum bulk charge density allowed by the applied doping concentration, N in the depletion region of the ith AlGaN barrier or potential well created by the charge sheet _Di And N _Ai The donor and acceptor concentrations in the ith AlGaN barrier or well, respectively, and e is the fundamental charge level.

Optionally, at least one of the AlGaN barriers includes an AlGaN front barrier spacer (priority-barrier spacer), an AlGaN back barrier spacer (post-barrier spacer), and an AlGaN main barrier (main barrier) interposed between the AlGaN front barrier spacer and the AlGaN back barrier spacer, wherein an Al composition of the AlGaN front barrier spacer and an Al composition of the AlGaN back barrier spacer are different from an Al composition of the AlGaN main barrier, and a thickness of the AlGaN front barrier spacer and a thickness of the AlGaN back barrier spacer are smaller than a thickness of the AlGaN main barrier.

Alternatively, the thickness of the AlGaN front barrier isolation layer and the thickness of the AlGaN back barrier isolation layer are in the range of 0.1nm to 1.5 nm.

Alternatively, the Al composition of the AlGaN front barrier layer and the Al composition of the AlGaN rear barrier layer are higher than the Al composition of the AlGaN main barrier.

Alternatively, the AlGaN front barrier layer and the AlGaN rear barrier layer are made of AlN and have thicknesses in the range of 0.26-0.52nm, respectively.

Alternatively, the Al composition of the AlGaN front barrier layer and the Al composition of the AlGaN back barrier layer are lower than the Al composition of the adjacent AlGaN potential well.

Alternatively, the AlGaN front barrier spacer and the AlGaN rear barrier spacer are made of GaN and have thicknesses in the range of 0.1-0.52nm, respectively.

Alternatively, the Al composition of the AlGaN front barrier layer is higher than the Al composition of the AlGaN main barrier, and the Al composition of the AlGaN back barrier layer is lower than the Al composition of the adjacent AlGaN potential well; or the Al component of the AlGaN back barrier isolation layer is higher than that of the AlGaN main barrier, and the Al component of the AlGaN front barrier isolation layer is lower than that of the adjacent AlGaN potential well.

The heterostructure may further include alternately stacked p-type doped AlGaN barriers and another p-type doped AlGaN barrier on which the p-type doped AlGaN potential well is formed, wherein the other p-type doped AlGaN barrier includes: a main barrier in contact with the last quantum barrier of the MQW active region of the light-emitting device or photodetector, and a back barrier isolation layer on which one of the p-type doped AlGaN barrier and the p-type doped AlGaN potential well is formed, which are alternately stacked.

A third aspect of the present invention provides a multiple quantum well structure for a light emitting device or photodetector, comprising alternately stacked AlGaN barriers and AlGaN potential wells, wherein a thickness of each of the AlGaN barriers and AlGaN potential wells satisfies:

wherein h is _i Is the thickness of the ith AlGaN barrier or potential well; sigma (sigma) _i Is the sheet charge density of the charge sheet on the surface of the ith AlGaN barrier or well that is oppositely charged relative to the net active dopant in the ith AlGaN barrier or well; ρ is _0i ＝eN _Di -eN _Ai Maximum bulk charge density, allowed by the applied doping concentration, N in the depletion region of the ith AlGaN barrier or potential well created by the charge thin layer _Di And N _Ai The donor and acceptor concentrations in the ith AlGaN barrier or well, respectively, and e is the fundamental charge level.

Optionally, one or more of the AlGaN potential wells includes an n-doped AlGaN front well spacer (priority-well spacer), an n-doped AlGaN back well spacer (post-well spacer), and an AlGaN main potential well (main well) sandwiched between the n-doped AlGaN front well spacer and the n-doped AlGaN back well spacer, wherein an Al composition of the n-doped AlGaN front well spacer and an Al composition of the n-doped AlGaN back well spacer are different from an Al composition of the AlGaN main potential well, and a thickness of the n-doped AlGaN front well spacer and a thickness of the n-doped AlGaN back well spacer are less than a thickness of the AlGaN main potential well and a thickness of an adjacent AlGaN barrier.

Optionally, the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are doped with Si respectively, and the doping concentration is 1.0-8.0X10 ¹⁸ cm ^-3 The AlGaN main potential well is undoped or doped with Si, and the doping concentration is less than 5.0X10 ¹⁷ cm ^-3 At least one of the AlGaN barriers is doped with Si at a doping concentration of 1.0-8.0X10 ¹⁸ cm ^-3 。

Alternatively, the thickness of the n-type doped AlGaN front well isolation layer and the thickness of the n-type doped AlGaN back well isolation layer are respectively in the range of 0.1nm to 0.52 nm.

Alternatively, the Al composition of the n-doped AlGaN front well spacer and the Al composition of the n-doped AlGaN back well spacer are higher than the Al composition of the adjacent AlGaN barrier.

Alternatively, the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are made of AlN and have thicknesses in the range of 0.1 to 0.52nm, respectively.

Optionally, the Al composition of the n-doped AlGaN front well spacer and the Al composition of the n-doped AlGaN back well spacer are lower than the Al composition of the AlGaN main potential well.

Alternatively, the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are made of GaN and have thicknesses in the range of 0.1 to 0.52nm, respectively.

Optionally, the Al composition of the n-doped front well spacer is higher than the Al composition of the adjacent AlGaN barrier, and the Al composition of the n-doped AlGaN back well spacer is lower than the Al composition of the AlGaN main potential well; or the Al component of the n-type doped AlGaN back well isolation layer is higher than the Al component of the AlGaN barrier, and the Al component of the AlGaN front well isolation layer is lower than the Al component of the AlGaN main potential well.

Alternatively, one of the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer is made of AlN and the other is made of GaN, and the thicknesses are respectively in the range of 0.1 to 0.52 nm.

The multiple quantum well structure may further include an undoped AlGaN barrier formed on one of the AlGaN potential wells on one side and in contact with the p-type structure of the light emitting device or photodetector on the other side.

Optionally, one or more of the AlGaN barriers comprises one or more thin layers of positive charge, and the distance between two adjacent thin layers of positive charge is greater than the depletion depth of the depletion region generated by either of the two adjacent thin layers of positive charge.

Alternatively, the positively charged thin layer is formed by Si delta-doping with a thin layer doping density of 10 or more ¹² cm ^-2 。

Alternatively, each AlGaN barrier containing a thin layer of positive charges includes a doping concentration of 1.0-8.0X10 ¹⁸ cm ^-3 Is separated by a thin layer of positive charge.

Alternatively, the thickness of the Si doped layer of each AlGaN barrier containing a thin layer of positive charges is in the range of 6 to 10nm, respectively, and the thickness of the undoped layer of each AlGaN barrier containing a thin layer of positive charges is in the range of 2 to 4nm, respectively.

Optionally, one or more of the AlGaN potential wells includes an n-type doped AlGaN front well isolation layer, an n-type doped AlGaN back well isolation layer, and an AlGaN main potential well sandwiched between the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer, wherein an Al composition of the n-type doped AlGaN front well isolation layer and an Al composition of the n-type doped AlGaN back well isolation layer are different from an Al composition of the AlGaN main potential well, and a thickness of the n-type doped AlGaN front well isolation layer and a thickness of the n-type doped AlGaN back well isolation layer are smaller than a thickness of the AlGaN main potential well and a thickness of an adjacent AlGaN barrier.

Optionally, the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are doped with Si, respectively, at a doping concentration of 1.0X10% ¹⁸ -8.0×10 ¹⁸ cm ^-3 The AlGaN main potential well is undoped or doped with Si, and the doping concentration is less than 5.0X10 ¹⁷ cm ^-3 At least one of the AlGaN barriers is doped with Si at a doping concentration of 1.0X10 ¹⁸ -8.0×10 ¹⁸ cm ^-3 。

A fourth aspect of the invention provides a heterostructure for a light emitting device or photodetector comprising an alternating stack of n-doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w N-well, wherein, N-type doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w The thickness of each of the N-wells satisfies the following:

wherein L is _i Is the ith Al _b Ga _1-b N potential barrier or Al _w Ga _1-w Thickness of N potential well, N _Di Is the ith Al _b Ga _1-b N potential barrier or Al _w Ga _1-w Donor concentration of N-well (in cm ^-3 In units).

Optionally, n-type doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w The N-well is doped with Si at a doping concentration of 8.0X10 ¹⁸ –2.0×10 ¹⁹ cm ^-3 And b-w is equal to or greater than 0.15.

Optionally, the n-type doped Al _b Ga _1-b One or more of the N barriers comprises a Si delta-doped region.

Optionally, at least one of the n-type doped Al _b Ga _1-b An N-type doped AlGaN front barrier isolation layer and an N-type doped AlGaN rear barrier isolation layer are respectively formed on two sides of the N barrier, wherein the Al component of the N-type doped AlGaN front barrier isolation layer and the Al component of the N-type doped AlGaN rear barrier isolation layer are different from at least one N-type doped Al _b Ga _1-b The Al component of the N potential barrier, and the thickness of the N-type doped AlGaN front potential barrier isolation layer and the thickness of the N-type doped AlGaN rear potential barrier isolation layer are smaller than that of the at least one N-type doped Al _b Ga _1-b The thickness of the N barrier.

Alternatively, the thickness of the n-type doped AlGaN front barrier spacer and the thickness of the n-type doped AlGaN rear barrier spacer are in the range of 0.1nm to 1.5 nm.

Optionally, the Al component of the n-doped AlGaN front barrier layer and the Al component of the AlGaN back barrier layer are higher than the at least one n-doped Al _b Ga _1-b The Al component of the N barrier.

Alternatively, the Al composition of the AlGaN front barrier layer and the AlGaN back barrier layer is lower than the adjacent n-doped Al _w Ga _1-w Al composition of the N-well.

Optionally, the Al component of the AlGaN front barrier layer is higher than the at least one n-doped Al _b Ga _1-b The Al component of the N potential barrier and the Al component of the AlGaN back potential barrier isolation layer is lower than that of the adjacent N-type doped Al _w Ga _1-w Al component of N potential well; or the Al component of the AlGaN back barrier isolation layer is higher than that of the at least one n-type doped Al _b Ga _1-b The Al component of the N potential barrier and the Al component of the AlGaN front barrier isolation layer is lower than that of the adjacent N-type doped Al _w Ga _1-w Al composition of the N-well.

A fifth aspect of the present invention provides a p-type contact structure for a light emitting device or photodetector, comprising:

a first AlGaN barrier;

a first AlInGaN well formed on the first AlGaN barrier;

a second AlGaN barrier formed on the first AlInGaN well; the method comprises the steps of,

a second AlInGaN well formed on the second AlGaN barrier;

wherein a difference between the Al composition of the first AlGaN barrier and the Al composition of the first AlInGaN well is equal to or greater than 0.6, and a difference between the Al composition of the second AlGaN barrier and the Al composition of the second AlInGaN well is equal to or greater than 0.6.

Optionally, at least one of the first AlGaN barrier and the second AlGaN barrier is made of AlN.

Optionally, at least one of the first AlInGaN well and the second AlInGaN well is composed of In _x Ga _1-x N, wherein x is equal to or less than 0.3.

Alternatively, the thickness of the first AlGaN barrier and the thickness of the second AlGaN barrier are each in the range of 0.26 to 2.0 nm.

Optionally, the thickness of the first AlInGaN well and the thickness of the second AlInGaN well are each in the range of 0.52-3.0 nm.

Optionally, the first AlInGaN well is doped p-type with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 And the second AlInGaN well is doped n-type with a doping concentration of 1.0X10 ¹⁹ –1.5×10 ²⁰ cm ^-3 。

Alternatively, the first AlGaN barrier is p-doped with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 And the second AlGaN barrier is doped p-type with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 。

The p-type contact structure may further include an AlGaN layer on which the first AlGaN barrier is formed, wherein the AlGaN layer on which the first AlGaN barrier is formed has an Al composition lower than that of the first AlGaN barrier and is in the range of 0.5-0.65, has a thickness in the range of 2.0-5.0nm, and is p-type doped with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 。

A sixth aspect of the present invention provides a light emitting device comprising:

a light emitting device comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

an active region sandwiched between the n-type AlGaN structure and the p-type AlGaN structure,

wherein the p-type AlGaN structure comprises a heterostructure according to the first aspect of the invention.

A light emitting device comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the p-type AlGaN structure comprises a heterostructure according to the second aspect of the invention.

A light emitting device comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the active region comprises a multiple quantum well structure according to the third aspect of the present invention.

A light emitting device comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the n-type AlGaN structure comprises a heterostructure according to the fourth aspect of the invention.

A light emitting device comprising:

an n-type AlGaN structure;

a p-type AlGaN structure;

an active region sandwiched between the n-type AlGaN structure and the p-type AlGaN structure; the method comprises the steps of,

a p-type contact structure according to the fifth aspect of the present invention formed on a p-type AlGaN structure.

The heterostructures, the multiple quantum well structures and the p-type contact structures according to the above first to fifth aspects of the present invention may be applied to any suitable light emitting device or photodetector, alone or in any combination thereof.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. Throughout the drawings, like reference numerals denote like elements, and layers may denote a set of layers that are functionally related to each other.

Fig. 1 shows a thin layer of positive charge (via n-type delta doping) inserted into a thick p-type doped semiconductor;

FIG. 2 shows a p-type doped heterostructure with thin layers of opposite charge generated by polarization discontinuities;

fig. 3A plots a thin layer of positive charge (σ=10) inserted into p-type semiconductors with different activation dopant levels ¹³ e·cm ^-2 ) A peripheral potential curve;

FIG. 3B plots absolute values of the maximum potential drop generated by a thin layer of positive charges inserted into p-type semiconductors with different levels of active dopants;

FIG. 4 plots depletion depth curves for different sheet charge densities and activation dopant levels;

FIG. 5A schematically shows the Al after full relaxation _y Ga _1-y Full strain Al grown on N-thick templates _x Ga _1-x The interfacial polarization sheet charge of the N-thin film;

FIG. 5B depicts a fully relaxed Al in a thick _y Ga _1-y Full strain grown Al on N template _x Ga _1-x The charge density of the polarized thin layer obtained by calculation of the N thin film is less than or equal to x;

FIG. 5C depicts a fully relaxed Al in a thick _y Ga _1-y Full strain grown Al on N template _x Ga _1-x The charge density of the polarized thin layer obtained by calculation of the N thin film is equal to or greater than x;

FIG. 6A schematically shows In after full relaxation _y Ga _1-y Full strain In grown on N thick templates _x Ga _1-x The interfacial polarization sheet charge of the N-thin film;

FIG. 6B depicts a full relaxation In at thick _y Ga _1-y Full strain grown In on N template _x Ga _1-x The charge density of the polarized thin layer obtained by calculation of the N thin film is less than or equal to x;

FIG. 6C depicts a full relaxation In at thick _y Ga _1-y Full strain grown In on N template _x Ga _1-x The charge density of the polarized thin layer obtained by calculation of the N thin film is equal to or greater than x;

FIG. 7 shows a cross-sectional view of an LED according to one embodiment of the invention;

FIG. 8 shows a cross-sectional view of a p-type AlGaN structure according to one embodiment of the invention;

FIG. 9A illustrates one possible combination of dopant and composition distribution for the p-type AlGaN structure shown in FIG. 8;

FIG. 9B shows an energy band diagram of the p-type AlGaN structure shown in FIG. 9A;

fig. 10 shows a cross-sectional view of a p-type AlGaN structure according to another embodiment of the invention;

FIG. 11 shows a cross-sectional view of a p-type AlGaN heterostructure according to one embodiment of the present invention;

FIG. 12A illustrates one possible combination of dopant and composition distribution for the p-type AlGaN heterostructure illustrated in FIG. 11;

FIG. 12B shows an energy band diagram of the p-type AlGaN heterostructure shown in FIG. 12A;

FIG. 13 shows a cross-sectional view of a p-type AlGaN heterostructure according to one embodiment of the present invention;

FIG. 14A illustrates one possible combination of dopant and composition distribution for the p-type AlGaN heterostructure illustrated in FIG. 13;

FIG. 14B shows an energy band diagram of the p-type AlGaN heterostructure shown in FIG. 14A;

FIG. 15 shows a cross-sectional view of a p-type AlGaN heterostructure according to one embodiment of the present invention;

FIG. 16A illustrates one possible combination of dopant and composition distribution for the p-type AlGaN heterostructure illustrated in FIG. 15;

FIG. 16B shows an energy band diagram of the p-type AlGaN heterostructure shown in FIG. 16A;

FIG. 16C illustrates one possible combination of dopant and composition distribution for the p-type AlGaN heterostructure illustrated in FIG. 15;

FIG. 16D illustrates one possible combination of dopant and composition distribution for the p-type AlGaN heterostructure illustrated in FIG. 15;

FIG. 17 shows a cross-sectional view of an MQW structure according to an embodiment of the invention;

FIG. 18A illustrates one possible combination of dopant and component distribution for the MQW structure shown in FIG. 17;

FIG. 18B shows an energy band diagram of the MQW structure shown in FIG. 18A;

FIG. 19A shows dopant and composition distribution of a prior art AlGaN/AlGaN MQW;

FIG. 19B shows an energy band diagram of the prior art AlGaN/AlGaN MQW shown in FIG. 19A;

FIG. 20 shows a cross-sectional view of an MQW structure according to an embodiment of the invention;

FIG. 21A illustrates one possible combination of dopant and component distribution of the MQW 30 shown in FIG. 20;

FIG. 21B illustrates one possible combination of dopant and component distribution of the MQW 30 shown in FIG. 20;

FIG. 21C illustrates one possible combination of dopant and component distribution of the MQW 30 shown in FIG. 20;

FIG. 22 shows a cross-sectional view of an n-type AlGaN heterostructure according to one embodiment of the present invention;

FIG. 23A illustrates one possible combination of dopant and composition distribution for the n-type AlGaN heterostructure illustrated in FIG. 22;

FIG. 23B shows an energy band diagram of the n-type AlGaN heterostructure shown in FIG. 23A;

FIG. 24 shows a cross-sectional view of an n-type AlGaN heterostructure according to one embodiment of the present invention;

FIG. 25 illustrates a cross-sectional view of a p-type AlGaN/n-type AlInGaN heterostructure in accordance with one embodiment of the present invention;

fig. 26A shows one possible combination of dopant and composition distribution for the p-type AlGaN/n-type AlInGaN heterostructure shown in fig. 23;

fig. 26B shows the energy band diagram of the p-type AlGaN/n-type AlInGaN heterostructure shown in fig. 26A.

Detailed Description

Throughout the specification, the term "group III nitride" generally refers to a metal nitride having a cation selected from group IIIA of the periodic table of elements. That is, III-nitrides include AlN, gaN, inN and their ternary (AlGaN, inGaN, inAlN) and quaternary (AlInGaN) alloys. In the present specification, if one element of the group III elements is so small that its presence is common to the bulk material properties, e.g., lattice constant The number, band gap and conductivity have little or negligible effect, and the quaternary element may be reduced to ternary for simplicity. For example, if the In composition In a quaternary AlInGaN is extremely small, less than 1%, then the AlInGaN quaternary can be reduced to ternary AlGaN. Similarly, if one of the group III elements is extremely small, the ternary can be reduced to binary. For example, if the In composition In a ternary InGaN is very small, less than 1%, then the InGaN ternary may be reduced to binary GaN. The group III nitride may also include a small amount of transition metal nitride, such as TiN, zrN, hfN having a mole fraction of no more than 10%. For example, the group III nitride or nitrides may include Al _x In _y Ga _z Ti _(1-x-y-z) N、Al _x In _y Ga _z Zr _(1-x-y-z) N、Al _x In _y Ga _z Hf _(1-x-y-z) N, wherein, (1-x-y-z) is less than or equal to 10%.

The semiconductor may be doped with a donor or acceptor and is referred to as an n-type or p-type doped semiconductor or an n-or p-semiconductor, respectively. The donor and acceptor release carrier electrons and holes, respectively, into the host semiconductor, and thus the activated or ionized donor and acceptor are positive and negative fixed charged ions, respectively, located in the host semiconductor lattice.

Typically, two semiconductors epitaxially formed from each other having different bandgap widths (and typically also different lattice constants) form a heterostructure. Light emitting devices such as Light Emitting Diodes (LEDs) and laser diodes employ many heterostructures for strain management, dislocation blocking, carrier confinement and light generation. Two special heterostructures, namely quantum wells and superlattices, are widely used in LEDs. In general, a light emitting device such as an LED may include an n-type AlGaN structure made of an n-type AlGaN heterostructure, a p-type AlGaN structure made of a p-type AlGaN heterostructure, and a light emitting heterostructure active region made of a Multiple Quantum Well (MQW) sandwiched between the n-type AlGaN structure and the p-type AlGaN structure.

In the following, a wurtzite c-plane ((0002) plane) nitride light emitting device or structure is used as an example to clarify the principle and spirit of the present invention. The teachings presented in this specification and in the examples below can be applied to non-c-plane nitride semiconductors, II-VI semiconductors, and other semiconductor devices.

Fig. 1 shows a thin layer of positive charge inserted into a thick p-type doped semiconductor that is a thick layer of p-type doped (e.g., mg doped) AlGaN according to an embodiment of the invention. Here, the positive sheet charge may be obtained via n-type delta doping, typically via simultaneous turning on of the n-type dopant source and the group V source (e.g., ammonia or nitrogen) when the group III source (e.g., al and Ga) is turned off during AlGaN epitaxial growth. N-type dopants, such as Si, O or Ge atoms, occupy Al and/or Ga lattice sites in AlGaN, act as donors, and ionize into a positive fixed charge via the release of mobile carrier electrons. Likewise, negative sheet charge can be obtained via p-type delta doping by turning on both the p-type dopant source and the group V source simultaneously when the group III source is turned off during AlGaN epitaxial growth. P-type dopants, such as Mg atoms, occupy Al and/or Ga lattice sites in AlGaN, acting as acceptors, ionizing into a negative fixed charge via release of mobile carrier holes. In practice delta doping can also be equivalently achieved via heavily doping a very thin layer. For example, a 2nm thick layer is doped to 5X 10 ¹⁹ cm ^-3 Or doping a 1nm thick layer to 10 ²⁰ cm ^-3 Equivalent to a sheet density of 10 ¹³ cm ^-2 Delta doping of (a).

Referring to fig. 1, considering the bilateral symmetry around the charge of the thin layer and assuming that the lateral size of the charge thin layer is much larger than the distance (r) to the charge of the thin layer, the charge thin layer is regarded as an infinite charge thin layer, and the electric field strength E (r) and the electric potential U (r) near the charge thin layer can be calculated using the gaussian theorem.

The method comprises the steps of,

wherein σ, ε, ρ, r and e are eachThe sheet charge areal density, the dielectric constant of the bulk AlGaN layer, the bulk charge density, the distance to the sheet charge, and the fundamental charge level. In doped semiconductors, the bulk charge density is the net charge density generated by the activated donor and acceptor, i.e.,

wherein (1)>

p and n are the concentrations of ionized donor, acceptor, free hole and electron, respectively. In the neutral region, the bulk charge density is zero. In the depletion region (free carriers are not allowed),>

note that, in the depletion region,

this is due to the dopant activation energy being greater than the thermal energy resulting in a dopant under-activation (where N _D And N _A Donor and acceptor dopant concentrations, respectively).

If the charge sheet is oppositely charged relative to the net active dopant, the charge sheet will enhance the activation of the dopant via electrically repelling carriers away from the dopant. This creates a carrier depletion region around the charge sheet. Boundary r between depletion region and neutral region ₀ Where the electric field is zero (E (r) =0), given by the following formula:

then depletion depth L _d The method comprises the following steps:

when the charge density of the thin layer is 10 ¹¹ -10 ¹⁴ e·cm ^-2 The depletion depth profile calculated using equation 5 is shown in fig. 4 for different bulk charge concentrations as the range varies. It can be seen that the depletion depth can range from sub-nanometers to several hundred nanometers, depending on the charge distribution.

Maximum potential drop DeltaU _max Occurs at the depletion edge, where,

the maximum potential drop may be large, hopefully enhancing the activation of deep acceptors in wide bandgap materials such as AlGaN. In fig. 3A, different bulk charge densities (ρ= -5 x 10) are plotted ¹⁸ 、-1×10 ¹⁹ 、-2×10 ¹⁹ e·cm ^-3 ) Is (sigma=10) ¹³ e·cm ^-2 ) Some potential curves around. As can be seen, a maximum potential drop of a few hundred millielectron volts (meV) is achieved. More generally, the absolute value of the maximum potential drop predicted by equation 6 is plotted in fig. 3B. In conjunction with fig. 3B and 4, for vertical conduction, it is desirable to have a large maximum potential drop and a small depletion depth. This can be achieved by using a high sheet charge density and a high dopant concentration. For example, for σ=4×10 ¹³ e·cm ^-2 And

the depletion depth was only 2nm and the maximum potential drop was 213meV. This will greatly enhance deep acceptor activation within the AlGaN material. For sigma not less than 6X 10 ¹³ cm ^-2 The maximum potential drop will exceed 500meV, regardless of the dopant level. This means that even heavily Mg doped AlN will have surface hole accumulation and become conductive because the Mg acceptors in AlN have an activation energy of about 500meV.

As mentioned previously, the charge sheet may be realized via delta doping,thus, n-type and p-type delta doping can introduce positive and negative sheet charges, respectively. Another way to obtain a thin layer of charge is to introduce a polarization discontinuity, because

(/>

And->

Polarization and surface normal vectors, respectively), any discontinuity in the polarization vector at the interface may create an interface sheet charge. In fig. 2, three infinite charge lamellae are shown inserted into p-doped AlGaN, one positive charge lamella in the center and two negative charge lamellae at the edges. This can be achieved by sandwiching an AlGaN heterostructure between two AlGaN layers of higher Al content. In general, acceptor activation can be assisted as long as the electric field generated by the charge sheet is sufficiently strong. More specifically, according to the present invention, an acceptor will be fully activated if the maximum potential drop is close (within thermal energy) or greater than the acceptor activation energy and the depletion depth is less than a few nanometers to allow quantum tunneling. Upon activation, free holes are pushed away from the positively charged thin layer to the negatively charged thin layer, resulting in hole accumulation or formation of two-dimensional hole gas (2 DHG) in the vicinity of the negatively charged thin layer.

By symmetry, the AlGaN heterostructure shown in fig. 2 may be n-doped instead of p-doped, even though not explicitly shown. In this case, the donor will be fully activated if the maximum potential drop is close (within thermal energy) or greater than the donor activation energy and the depletion depth is within a few nanometers to allow quantum tunneling. Upon activation, free electrons are pushed away from the thin layer of negative charge to the thin layer of positive charge, resulting in electron accumulation or formation of a two-dimensional electron gas (2 DEG) in the vicinity of the thin layer of positive charge.

In accordance with one aspect of the present invention, to maximize electric field assisted dopant activation and carrier accumulation, the thickness (h _i ) Preferably, the inequality is satisfied:

wherein, the liquid crystal display device comprises a liquid crystal display device,

is the bulk charge density in the depletion region of the ith layer (+)>

And->

Are the respective ionized donor and acceptor concentrations therein), σ _i Is the sheet charge density on the surface of the i-th layer, which is opposite to the net activated dopant therein (ρ _i ) Oppositely charged, and ρ _0i ＝eN _Di -eN _Ai Is the maximum charge density (N _Di And N _Ai Is the respective donor and acceptor concentrations of the i-th layer).

The basic requirement of the inequality given by equation 7 is the thickness (h _i ) At sigma of _i And ρ _0i Within or at the boundary of the depletion region generated to ensure maximum dopant activation within the ith layer and to form carrier accumulation on one surface of the ith layer.

FIG. 5A shows a simple AlGaN heterostructure with surface normal pointing to [0002]Orientation, and contains thick fully relaxed Al _x Ga _1-x N template and thin full strain Al _y Ga _1-y N, i.e. Al _y Ga _1-y N is formed in Al with full strain _x Ga _1-x And N. Due to the composition differences, there is an interfacial sheet charge caused by piezoelectric and spontaneous polarization. Using the parameters given by E.T.Yu et al ("Spontaneous and piezoelectric polarization in nitride heterostructures" by E.T.Yu, chair 4, III-V Nitride Semiconductors: applications and Devices, suite by E.T.Yu, and O.Manassch, published in 2003by Taylor)&Francis), for y.gtoreq.x and y.gtoreq.x, calculate Al respectively _y Ga _1-y N/Al _x Ga _1-x N interface charge density (σ) and plotted in fig. 5B and 5C.

In FIG. 5B, where y.gtoreq.x, means that the high Al composition AlGaN film is formed on the low Al composition thick AlGaN template with full strain, generating positive interface sheet charges at the interface. In FIG. 5C, where y.ltoreq.x, means that the AlGaN thin film of low Al composition is formed on the thick AlGaN template of high Al composition with full strain, generating negative sheet charge at the interface. For this simple heterostructure, the interfacial sheet charge density can be roughly described by the following formula:

Where y and x are the Al components of the AlGaN thin film and the thick AlGaN template, respectively.

FIG. 6A shows a simple InGaN heterostructure with surface normal pointing to [0002]Direction and contain thick fully relaxed In _x Ga _1-x N template and thin full strain In _y Ga _1-y N, i.e. In _y Ga _1-y N is formed In full strain _x Ga _1-x And N. For y is larger than or equal to x and y is smaller than or equal to x, respectively calculating In _y Ga _1-y N/In _x Ga _1-x N interface charge density (σ), and is plotted in fig. 6B and 6C.

In FIG. 6B, where y.gtoreq.x, means that the high In composition InGaN thin film is formed with full strain on the low In composition thick InGaN template, creating a negative sheet charge at the interface. In FIG. 6C, where y.ltoreq.x, means that the low In composition InGaN thin film is formed with full strain on the high In composition thick InGaN template, creating a positive sheet charge at the interface. The interfacial sheet charge density can be roughly described by the following formula:

where y and x are the In composition of the InGaN film and the thick InGaN template, respectively.

With equations 6-9, better AlGaN/AlGaN and InGaN/InGaN heterostructures can be designed for light emitting devices.

In fig. 7 a schematic cross-sectional view of a UV LED 1 according to another aspect of the invention is shown. The structure starts with a substrate 10, which substrate 10 is preferably UV transparent and may be selected from sapphire, alN, siC, etc. A thin buffer layer 21 made of AlN or AlGaN having a high Al composition is formed on the substrate 10. A thick template 22 is then formed on the buffer layer 21. Template 22 may be made of a thick layer of AlN or AlGaN of high Al composition, for example, 0.3-4.0 μm thick. Even though not shown in fig. 7, a strain management structure, such as an Al composition graded AlGaN layer or sets of AlN/AlGaN superlattices, may be formed on the template 22. A thick n-AlGaN layer 23 for current spreading, which is formed of a thickness of 2.0-5.0 μm (such as 3.0 μm) and a dopant concentration of 2.0×10, is formed on the template 22 ¹⁸ –5.0×10 ¹⁸ cm ^-3 Is made of Si or Ge doped AlGaN. Forming heavily N-doped N on N-AlGaN layer 23 ⁺ AlGaN heterostructure 24. Heterostructure 24 can be n-doped to 8 x 10 ¹⁸ -2×10 ¹⁹ cm ^-3 And its design will be disclosed in detail in the following. Forming thin lightly doped N on heterostructure 24 ^- AlGaN layer 25 (0.1-0.5 μm, such as 0.15 μm, n=2.5×10) ¹⁷ -2×10 ¹⁸ cm ^-3 ) To reduce current blocking and to prepare for uniform current injection into subsequent Al _b Ga _1-b N/Al _w Ga _1-w In the N MQW active region 30. MQW 30 is made of n-Al alternately stacked a plurality of times _b Ga _1-b N barrier and Al _w Ga _1-w N-well formation is, for example, 3-8 times. The barrier thickness ranges from 8.0 to 16.0nm and the potential well thickness ranges from 1.0 to 5.0nm. The total thickness of the MQW 30 is typically less than 200nm, for example 75nm, 100nm or 150nm. n-Al _b Ga _1-b N barrier and Al _w Ga _1-w The N-well may have Al composition in the range of 0.3-1.0 and 0.0-0.85, respectively, and the barrier and adjacent well differ in Al composition by at least 0.10, 0.15, 0.2, 0.25 or 0.3 (i.e., b-w.gtoreq.0.10, 0.15, 0.2, 0.25 or 0.3), or to ensure a barrier-well bandgap width difference (ΔE) _g ) At least 270meV to ensure quantaAnd (3) a finite field effect. Further disclosure regarding MQW 30 will be provided in connection with fig. 17, 18A, 18B, 20, 21A, 21B, and 21C. Following the MQW 30 is a p-type AlGaN heterostructure 40, the structure of which will be disclosed in detail below. Typical functionalities of heterostructure 40 include electron blocking, hole supply, and hole injection. Another AlInGaN heterostructure 498 is formed over the heterostructure 40, which acts as a p-type contact layer. Heterostructure 498 is disclosed in detail below.

As also seen in fig. 7, an n-ohmic contact 51 is formed on the heavily n-doped heterostructure 24. It may be made of a stack of thin metal layers, such as titanium/aluminum/titanium/gold (Ti/Al/Ti/Au), with a corresponding layer thickness of 3-40/70-80/10-20/80-100nm, e.g. 35/75/15/90nm. It can also be made of thin vanadium/aluminum/vanadium/gold (V/Al/V/Au) with a corresponding layer thickness of 3-80/70-150/10-50/20-800nm, e.g. 20/100/20/60nm. An n-contact 52 and an n-contact pad 5 are formed on the n-ohmic contact 51, which is made of a thick metal layer (such as a 2-5 μm thick gold layer). Likewise, a p-ohmic contact 61 is formed on the heterostructure 498 and is in contact with the heterostructure 498. The metal scheme of the p-ohmic contact 61 will be disclosed in connection with the heterostructure 498 below. A p-contact 62 and a p-contact pad 6 are formed on the p-ohmic contact 61, which is made of a thick metal layer, such as a 2-5 μm thick gold layer. The entire LED structure is then passivated by a passivation layer 70 except for the n-contact pad 5 and p-contact pad 6 (passivation layer 70 also covers the device sidewalls, even though not explicitly shown in fig. 7). The passivation layer 70 is preferably made of a material such as SiO ₂ 、Al ₂ O ₃ 、AlF ₃ 、CaF ₂ And MgF ₂ And an UV transparent dielectric.

A p-type AlGaN heterostructure 40 according to an embodiment of the invention is shown in fig. 8. In this embodiment, heterostructure 40 includes Mg doped AlGaN layer 401 intercalated with a plurality of thin layers 402 of positive charges. The thin layer of positive charge 402 is formed via donor dopant delta doping (e.g., si delta doping). Fig. 9A shows a possible combination of dopant and composition distribution of the heterostructure 40 shown in fig. 8, wherein the Mg doping and Al composition of the AlGaN layer 401 is constant and the sheet charge density of the sheet 402 is also constant. Fig. 9B shows an energy band diagram of the p-type AlGaN heterostructure 40 shown in fig. 9A. In other embodiments, the Mg doping and Al composition may not be constant, i.e., they may vary along the epitaxial direction. For example, mg doping and Al composition may decrease or increase along the epitaxial direction. Moreover, the sheet charge density of different sheets 402 may be different.

Referring to fig. 9B, the present invention requires that the distance between adjacent lamellae 402 be greater than the maximum depletion depth (L) given by equation 5 _d0 ) I.e.,

where σ is the sheet charge density generated by Si delta-doping, which is the product of Si delta-doped sheet density and the fundamental charge level, and ρ ₀ Is the product of the acceptor doping concentration and the charge capacity of the electrons (ρ ₀ ＝-eN _A ). This requirement ensures that adjacent depletion regions of adjacent thin layers 402 do not overlap and that the entire heterostructure 40 is not depleted. Moreover, the maximum depletion depth around the thin layer 402 is less than 10nm, e.g., less than 5nm or less than 2nm, allowing sufficient carrier tunneling or diffusion once an external bias is applied to the heterostructure 40. These requirements set the design rules of heterostructure 40 for the bulk acceptor dopant concentration, thin layer donor dopant density, and thin layer donor spatial arrangement of the heterostructure.

Donor delta doping density in heterostructure 40 is 1 x 10 ¹¹ -1×10 ¹³ cm ^-2 Within a range of, for example, 5X 10 ¹¹ -5×10 ¹² cm ^-2 Or equivalent. For example, for a thickness of 1nm, it may be equivalent to 1X 10 ¹⁸ -1×10 ²⁰ cm ^-3 Is a bulk doping concentration of (c). Also, the higher the Mg dopant concentration, the greater the Si delta-doping density allowed in the heterostructure 40, provided that the design rules set forth above are satisfied. For example, referring to FIG. 4, if the depletion depth is allowed to be 2nm thick, then 2X 10 ¹⁹ cm ^-3 The bulk Mg doping level in layer 402 allows a maximum Si layer density of about 3.9x10 ¹² cm ^-2 And adjacent lamellae 402 are placed more than 2nm (e.g., 5 or 10 nm) apart from each other.

According to an embodiment of the invention, positive charges are impartedThe insertion of a thin layer (via donor delta doping) into the p-type heterostructure 40 can improve the reliability of the UV LED. It is well known that p-type dopants in group III nitrides can attract the incorporation of hydrogen atoms. These hydrogen atoms occupy interstitial sites of the nitride lattice and are often positively charged, i.e., become H ⁺ . Gap H in p-type nitride when nitride LED is forward biased and in operation ⁺ Potential energy can be obtained which is inevitably converted into kinetic energy and drives H ⁺ Moving toward the MQW active region. Ions in the MQW active region may scatter carriers and reduce the probability of radiative recombination, resulting in reduced light output efficiency. If the gap H ⁺ This situation is exacerbated by high concentrations, high electric field strengths, and poor material quality. These are precisely the case of AlGaN-based UV LEDs, compared to GaN-based visible LEDs. The insertion of multiple thin layers of positive charges in the p-nitride slows down the gap H ⁺ And improves the reliability of the LED.

The heterostructure 40 shown in fig. 8 is a single p-type AlGaN layer with one or more thin layers of positive charge interposed.

Heterostructure 40 may also comprise more than one p-AlGaN layer, which is intercalated with multiple thin layers of positive charges. In fig. 10, a heterostructure 40 is shown comprising three Mg doped AlGaN layers 403, 404 and 405, each of which is intercalated with one or more thin layers of positive charge (4032, 4042 and 4052), and the thin layers of positive charge (4032, 4042 and 4052) divide each Mg doped

AlGaN layer

403, 404 and 405 into a plurality of regions (4031, 4041 and 4051), respectively. The thickness, composition, doping and thin layers of positive charges of AlGaN layers 403, 404 and 405 may be different from each other. For example, if AlGaN layer 403 is closest to MQW active region 30, alGaN layer 403 may be thickest, having the highest Al composition and the most thin layer of positive charge. In heterostructure 40 AlGaN layer 404 may have a second or third highest Al composition. However, each of the AlGaN layers 403, 404 and 405 still follows the design rules outlined previously, i.e. the distance between adjacent thin layers of positive charge should be greater than the maximum depletion depth, and the maximum depletion depth should be less than 10nm, for example less than 5nm or less than 2nm.

In fig. 11, a p-type AlGaN heterostructure 40 according to another embodiment of the present invention is shown, comprising an Mg doped high Al composition AlGaN layer 41 (which may have an Al composition in the range of 0.6-0.8 and a thickness in the range of 1.0-5.0 nm), more than one Mg doped AlGaN layer (42, 44, 46 and 48) intercalated with at least one positively charged thin layer (422, 442, 462 and 482), and more than one Mg doped AlGaN layer (43, 45, 47 and 49) separating AlGaN layers 42, 44, 46 and 48. The thin layers of

positive charges

422, 442, 462 and 482 divide the respective AlGaN layers (42, 44, 46 and 48) into thinner front regions (421, 441, 461 and 481) and thicker rear regions (423, 443, 463 and 483). In this embodiment, the Al composition and Mg doping may be constant within one AlGaN layer, however, the Al composition and layer thickness of different AlGaN layers are typically different. In special cases, alGaN layers 42-49 may form a periodic structure (such as a superlattice), where layers 42, 44, 46, and 48 may be barrier layers with a higher Al composition (e.g., 0.60-0.85), and layers 43, 45, 47, and 49 may be potential well layers with a lower Al composition (e.g., 0.50-0.70), and vice versa. The previously outlined sheet charge design rules still apply to the positively charged

sheets

422, 442, 462 and 482, i.e., the distance between adjacent positively charged sheets should be greater than the maximum depletion depth and the maximum depletion depth should be less than 10nm, e.g., less than 5nm or less than 2nm. The different AlGaN layers 42, 44, 46 and 48 may have the same or different Al composition and thickness, and the different AlGaN layers 43, 45, 47 and 49 may have the same or different Al composition and thickness.

Fig. 12A shows one possible combination of dopant and composition distribution of heterostructure 40 shown in fig. 11, where Mg doping level within heterostructure 40 is constant and the Al composition of AlGaN layers 42, 44 and 46 is high forming a barrier layer, the Al composition of AlGaN layers 43, 45 and 47 is low forming a potential well layer, and thin layers of positive charge (422, 442 and 462) are located within the barrier layer. Except for the thin layer of positive charge (sigma) created by Si delta-doping ₃ ) In addition, there is also a thin layer of charge (σ) caused by polarization discontinuity at the AlGaN barrier/well interface ₀ ,-σ ₀ ). Fig. 12B shows an energy band diagram of the p-type AlGaN heterostructure 40 shown in fig. 12A.

A p-type AlGaN heterostructure 40 according to another embodiment of the present invention is shown in fig. 13, which includes an Mg doped Al composition modulated AlGaN heterostructure. Specifically, it is formed by alternately stacking AlGaN potential barriers (42 ", 44", 46 "and 48") having an Al composition in the range of 0.60 to 0.85 and AlGaN potential wells (43 ", 45", 47 "and 49") having an Al composition in the range of 0.50 to 0.70. The different AlGaN barriers may have the same or different Al composition and thickness, and the different AlGaN potential wells may have the same or different Al composition and thickness. Here, each potential barrier and each potential well may have different Al composition, doping concentration, and thickness. As previously discussed, for heterostructures with many individual layers, the thickness, doping and composition of each layer are not independent parameters, rather they satisfy the inequality given by equation 7 according to the present invention. Thus, the thickness L of the ith potential barrier _Bi The method meets the following conditions:

wherein σ as a function of component discontinuity (see equation 8) _Bi Is the thin layer charge density on the surface of the ith barrier, which is oppositely charged relative to the net active dopant within the ith barrier, and ρ _B0i ＝eN _BDi -eN _BAi Is the maximum charge density (N) in the doping-allowed barrier depletion region _BDi And N _BAi The respective donor and acceptor concentrations of the ith barrier). And thickness L of jth potential well _Wj The method meets the following conditions: />

Wherein σ as a function of component discontinuity (see equation 8) _Wj Is the sheet charge density on the surface of the jth potential well that is oppositely charged relative to the net active dopant in the jth potential well, and ρ _W0j ＝eN _WDj -eN _WAj Is the maximum charge density (N) in the well depletion region allowed by doping _WDj And N _WAj Is the respective donor and acceptor concentrations of the jth potential well).

The embodiment of the AlGaN heterostructure 40 shown in FIG. 13 is uniformly doped with a concentration ofN _A (cm ^-3 ) Al of Mg of (2) _b Ga _1-b N/Al _w Ga _1-w An N superlattice. Therefore, the barrier and potential well thicknesses according to equations 7 and 8 satisfy: l (L) _B 、

For example, if b-w=0.2 and N _A ＝10 ¹⁹ cm ^-3 L is then _B 、L _W Less than or equal to 5nm; if b-w=0.4 and N _A ＝2×10 ¹⁹ cm ^-3 L is then _B 、L _W 5nm, etc.

Fig. 14A shows doping and composition distribution for the special (i.e., superlattice) embodiment of the heterostructure 40 shown in fig. 13, where Mg doping may be constant or different for the potential barriers and wells within the heterostructure 40 (i.e., ρ _B0i ＝ρ _W0j Or ρ _B0i ≠ρ _W0j ). Fig. 14B shows an energy band diagram of the p-type AlGaN heterostructure 40 shown in fig. 14A.

Since the barrier layer of the heterostructure 40 is inclined by polarizing interface charges in such a manner as to hinder vertical transport of carriers, the barrier layer may be thinner than the potential well layer in the case where the vertical transport weight of carriers is greater than the quantum confinement.

A p-type AlGaN heterostructure 40 according to another embodiment of the present invention is shown in fig. 15. It differs from the embodiment shown in fig. 13 in the barrier layer. The heterostructure 40 shown in fig. 15 includes a first AlGaN barrier 42 'and more than one AlGaN barrier (shown as 44', 46', 48'). The first barrier 42' in contact with the last quantum barrier of the MQW active region comprises a main barrier 422' and a back barrier isolation layer 423'. The other barriers (44 ', 46', 48' as shown) contain main and front and back barrier isolation layers, respectively. For example, the second barrier 44 'includes a main barrier 442' and a front barrier isolation layer 441 'and a rear barrier isolation layer 443', and the third barrier 46 'includes a main barrier 462' and a front barrier isolation layer 461 'and a rear barrier isolation layer 463', and the like. The back barrier isolation layer is in contact with its main barrier and its next potential well, and the front barrier isolation layer is in contact with its previous potential well and its main barrier. For example, the back barrier isolation layer 423 'is in contact with its main barrier 422 and its next potential well 43'; the front barrier isolation layer 441' is in contact with its previous potential well 43' and its main barrier 442 '; the back barrier isolation layer 443' is in contact with its main barrier 442' and its next potential well 45', etc.

The back and front barrier spacers are made of p-type AlGaN having a different Al composition than the main barrier and potential well so that the main barrier and potential well can have different interface sheet charge densities, allowing greater flexibility in designing the heterostructure 40. The back barrier isolation layer and the front barrier isolation layer are thinner than the main barrier and the potential well. The back barrier isolation layer and the front barrier isolation layer may have the same composition or different compositions. The thicknesses of the back barrier isolation layer and the front barrier isolation layer are optionally in the range of 0.1nm to 1.5nm, such as 0.5nm to 1.2nm, respectively. The Al composition of the back barrier isolation layer and the front barrier isolation layer may be in the range of 0.0 to 1.0, such as 0.10 to 0.95, respectively. The Al component of the main barrier may be in the range of 0.60-0.85.

In one embodiment, the back barrier isolation layer and the front barrier isolation layer have a higher Al composition than their main barrier. The combination of doping and composition profile for this embodiment is shown in fig. 16A, and its energy band diagram is shown in fig. 16B. As can be seen, in this embodiment, the jth potential well is subjected to an interface charge density σ _Wj Which is greater than the interface charge density sigma experienced by the ith main barrier _Bi . This is true because the Al composition difference between the isolation layer and the potential well is greater than the Al composition difference between the isolation layer and the main barrier, and this will generate more sheet charge at the potential well-isolation layer interface according to equation 8. In this embodiment, the Mg acceptors in the potential well will have a higher probability of activation. In one embodiment according to this aspect of the invention, the back barrier isolation layer and the front barrier isolation layer are each made of an AlN layer 0.26-0.52nm thick. The AlN back barrier isolation layer and the front barrier isolation layer enhance the electron blocking capability, thereby improving the reliability of the LED.

In another embodiment, the Al composition of the back barrier isolation layer and the front barrier isolation layer (such as 0.0-0.6 or 0.2-0.4) is greater than the adjacent potential well(s)E.g., 0.5-0.7) low. The combination of doping and component distribution for this embodiment (energy band diagram not shown here) is illustrated in fig. 16C. In this embodiment, the jth potential well is subjected to an interface charge density σ _Wj Which is less than the interface charge density sigma experienced by the ith main barrier _Bi . This is true because the Al composition difference between the isolation layer and the main barrier is greater than the Al composition difference between the isolation layer and the potential well, according to equation 8. In this embodiment, the Mg acceptors in the main barrier will have a higher probability of activation. In one embodiment according to this aspect of the invention, the back barrier isolation layer and the front barrier isolation layer are each made of a GaN layer 0.1-0.52 (such as 0.2-0.4) nm thick. The GaN back barrier spacer and front barrier spacer increase the hole concentration within AlGaN structure 40, thereby increasing the internal quantum efficiency of the LED.

In yet another embodiment according to this aspect of the invention, the at least one back barrier isolation layer and/or front barrier isolation layer is made of a thin layer of AlGaN having an Al composition higher than the main barrier and the at least one back barrier isolation layer and/or front barrier isolation layer is made of a thin layer of AlGaN having an Al composition smaller than the potential well. One combination of doping and composition profile for this embodiment is shown in fig. 16D. Optionally, the at least one back barrier isolation layer and/or the front barrier isolation layer is made of AlN and the at least one back barrier isolation layer and/or the front barrier isolation layer is made of GaN, the thickness of which is in the range of 0.1-0.52 nm. Optionally, the at least one AlN spacer layer is placed closer to the MQW 30 than the at least one GaN spacer layer.

The thicknesses of the potential well and the main barrier of the above embodiments may still follow equation 7.

The MQW active region is a special AlGaN heterostructure. The doping and composition distribution of the prior art AlGaN MQW is shown in fig. 19A, and the energy band diagram is shown in fig. 19B. As can be seen, the interfacial polarization sheet charge σ ₀ The quantum well band edges are tilted to spatially separate the injected electrons from holes, resulting in lower luminous efficiency. The interfacial polarized sheet charge also tilts the energy band edge of the quantum barrier, resulting in an increase in the resistance to electron and hole injection.

As shown in fig. 17, another aspect of the present invention provides a MQW 30. The MQW 30 includes undoped or lightly Si doped (e.g., 1.0-5.0X10 ¹⁷ cm ^-3 ) At least one Quantum Well (QW) 33 and at least one first Quantum Barrier (QB) 32, a penultimate QB 34 formed on the first QB 32 and a final QB 32' formed on the second QB 34. The final QB 32' is undoped and is in contact with the final QW 33 on one side and with the p-AlGaN heterostructure 40 (or other suitable p-AlGaN layer or structure) on the other side. The first QB 32 comprises a uniform Si doping (n=1.0-8.0×10 ¹⁸ cm ^-3 ) Layer 321, si delta-doped thin layer 322, and undoped layer 323. The penultimate QB 34 comprises a uniform Si doping (n=1.0-8.0x10 ¹⁸ cm ^-3 ) Layer 321 and undoped layer 323. The thickness of

layers

321 and 323 are 6-10nm and 2-4nm, respectively. Doping and composition distribution of MQW 30 is shown in fig. 18A and energy band diagram is shown in fig. 18B, according to one embodiment of the invention. Assuming that layer 321 has a thickness t, it has a Si doping concentration N _D And Si delta-doped thin layer charge density sigma ₃ And QB/QW interface polarized thin layer charge density sigma ₀ Then equation 10 holds.

σ ₃ ＝σ ₀ -eN _D t (equation 10)

In one embodiment, the difference in Al composition between QB 32 and QW 33 is 0.1 (b-w=0.1, then equation 8, σ is used ₀ ＝5×10 ¹² e·cm ^-2 ) And layer 321 is 8nm thick doped with N _D ＝5×10 ¹⁸ cm ^-3 . According to equation 10 of the present invention, si delta-doped thin layer charge density is preferred. Since Si is a fairly shallow donor in AlGaN, in one embodiment of the invention, the Si delta-doping density in layer 322 is 10 ¹² cm ^-2 。

In another embodiment, the difference in Al composition between QB 32 and QW 33 is 0.15 (b-w=0.15, then equation 8, σ is used ₀ ＝7.5×10 ¹² e·cm ^-2 ) And layer 321 is 8nm thick doped with N _D ＝5×10 ¹⁸ cm ^-3 . According to equation 10 of the present invention, the Si delta-doped thin layer charge density isPreferably, the method is used. Since Si is a fairly shallow donor in AlGaN, the present invention requires a Si delta-doping density of 3.5X10 in layer 322 ¹² cm ^-2 。

In yet another embodiment, the difference in Al composition between QB 32 and QW 33 is 0.2 (b-w=0.2, then equation 8, σ is used ₀ ＝1.0×10 ¹³ e·cm ^-2 ) And layer 321 is 10nm thick doped with N _D ＝5×10 ¹⁸ cm ^-3 . According to equation 10 of the present invention, si delta-doped thin layer charge density is preferred. Since Si is a fairly shallow donor in AlGaN, the present invention requires a Si delta-doping density of 5.0X10 in layer 322 ¹² cm ^-2 。

The Al composition of QW 33, final QB 32', layer 321, and layer 323 may be in the range of 0.35-0.55, 0.55-0.65, and 0.55-0.65, respectively.

The MQW active region designed according to this aspect of the invention has higher light generation efficiency and lower device operating voltage.

Another embodiment of a MQW 30 according to this aspect of the invention is shown in fig. 20, comprising at least a first QB 32 "and a last QB 34" and a QW 33', the QW 33' comprising a main QW 330 sandwiched by a front QW isolation layer 331 and a rear QW isolation layer 332. Some doping and composition profiles of MQW 30 are shown in fig. 21A-21C. As can be seen, all of the first QB 32", front QW isolation layer 331 and rear QW isolation layer 332 are uniformly doped with Si (n=1.0-8.0x10 ¹⁸ cm ^-3 ) All of the primary QW 330 may be undoped or doped with less than 5.0 x 10 ¹⁷ cm ^-3 And finally QB 34 "is undoped. The rear QW isolation layer is in contact with its previous main QW 330 and its next QW, and the front QW isolation layer is in contact with its previous QB and its next main QW.

The rear QW spacer and the front QW spacer are made of n-type AlGaN with different Al compositions than QB and the main QW, so that QB and the main QW can have different interface sheet charge densities to allow greater flexibility in designing the MQW 30. The rear QW isolation layer and the front QW isolation layer are thinner than the main QWs and QBs. The rear QW isolation layer and the front QW isolation layer may have the same composition or different compositions. The thickness of the rear QW isolation layer and the front QW isolation layer is optionally in the range of 0.1nm to 0.52 nm.

In one embodiment, the rear QW isolation layer and the front QW isolation layer have a higher Al composition than QB. One combination of doping and composition profile for this embodiment is shown in fig. 21A. In one embodiment according to this aspect of the invention, the rear QW isolation layer and the front QW isolation layer are made of AlN layers 0.1-0.52nm thick.

In another embodiment, the rear QW isolation layer and the front QW isolation layer have a lower Al composition than the potential well. One combination of doping and composition profile for this embodiment is shown in fig. 21B. In one embodiment according to this aspect of the invention, the rear QW isolation layer and the front QW isolation layer are made of a GaN layer 0.1-0.52nm thick.

In yet another embodiment according to this aspect of the invention, at least one of the rear QW spacers and/or the front QW spacers is made of a thin layer of AlGaN having an Al composition higher than QB, and at least one of the rear QW spacers and/or the front QW spacers is made of a thin layer of AlGaN having an Al composition smaller than the main QW. One combination of doping and composition profile for this embodiment is shown in fig. 21C. Alternatively, at least one thin AlGaN spacer is made of AlN and at least one thin AlGaN spacer is made of GaN, the thickness of which is in the range of 0.1-0.52 nm.

The Al composition of the first QB 32", the last QB 34", the main QW 330, the front QW isolation layer 331 and the rear QW isolation layer 332 may be in the range of 0.55 to 0.65, 0.35 to 0.55, 0.0 to 1.0 and 0.0 to 1.0, respectively.

The MQW active region designed according to this aspect of the invention has high light generation efficiency and low optical power attenuation over time.

FIG. 22 shows N of an embodiment in accordance with another aspect of the invention ⁺ An AlGaN heterostructure 24 comprising a heavily Si doped Al composition modulated AlGaN heterostructure. In general, heterostructure 24 can be formed from multiple AlGaN layers of different Al composition and thickness, all of which are heavily Si doped to 8.0X10 ¹⁸ -2.0×10 ¹⁹ cm ^-3 . The doping and thickness of each individual layer follow equation 7, similar to the combination aboveThe discussion given in fig. 2 and 13.

N ⁺ Superlattice embodiments of the AlGaN heterostructure 24 may be implemented by Al _b Ga _1-b N barrier 240 and Al _w Ga _1-w The N-well 241 is alternately stacked a plurality of times to uniformly dope N with a concentration of N _D (cm ^-3 ) Is formed of Si. Therefore, the barrier and potential well thicknesses according to equations 7 and 8 satisfy: l (L) _B ；

For example, if b-w=0.2 and N _D ＝10 ¹⁹ cm ^-3 L is then _B ,L _W Less than or equal to 5nm; if b-w=0.2 and N _D ＝8×10 ¹⁸ cm ^-3 L is then _B ,L _W 6.25nm, etc.

Fig. 23A illustrates a superlattice embodiment of the heterostructure 24 illustrated in fig. 22 in which the Si doping level is constant within the heterostructure 24. Fig. 23B shows an energy band diagram of the AlGaN heterostructure 24 shown in fig. 23A.

Fig. 24 shows another superlattice embodiment of the heterostructure 24 made of a plurality of alternating stacks of potential barriers 242 and potential wells 243, wherein the potential barriers 242 contain Si delta-doped regions 2422.

Since the barrier layer of the heterostructure 24 is inclined by polarizing interface charges in such a manner as to hinder vertical transport of electrons, in the heterostructure 24, the barrier layer may be thinner than the potential well layer in the case where the carrier vertical transport weight is greater than the quantum confinement.

Similar to the embodiment shown in fig. 15, optionally, a front barrier isolation layer and a back barrier isolation layer (not explicitly shown in fig. 22 and 24) may be present before and after the

barriers

240 and 242. The back and front barrier spacers are made of n-type AlGaN having a different Al composition than the potential barriers and wells so that the potential barriers and wells can have different interface sheet charge densities to allow greater flexibility in designing the heterostructure 24. The back barrier isolation layer and the front barrier isolation layer are thinner than the potential barrier and the potential well. The back barrier isolation layer and the front barrier isolation layer may have the same composition or different compositions. The thicknesses of the back barrier isolation layer and the front barrier isolation layer are optionally in the range of 0.1nm to 1.5 nm.

In one embodiment, the back barrier isolation layer and the front barrier isolation layer have a higher Al composition than their main barrier. For example, the back barrier isolation layer and the front barrier isolation layer may be made of an AlN layer having a thickness of 0.26-0.52 nm.

In another embodiment, the back barrier isolation layer and the front barrier isolation layer have a lower Al composition than the potential well. For example, the back barrier isolation layer and the front barrier isolation layer may be made of a GaN layer 0.1-0.52nm thick.

In yet another embodiment according to this aspect of the invention, at least one of the back barrier spacers and/or the front barrier spacers is made of a thin layer of AlGaN having an Al composition higher than the potential barrier and at least one of the back barrier spacers and/or the front barrier spacers is made of a thin layer of AlGaN having an Al composition smaller than the potential well. Alternatively, at least one thin AlGaN spacer is made of AlN and at least one thin AlGaN spacer is made of GaN, the thickness of which is in the range of 0.1-0.52 nm.

In accordance with yet another aspect of the present invention, fig. 25 shows a schematic cross-sectional view of a heterostructure 498 that acts as the p-type contact layer of the UV LED 1 shown in fig. 7. Heterostructure 498 includes a heavily Mg doped layer including AlGaN layer 4981, alGaN barrier 4982, alInGaN well 4983 and AlGaN barrier 4984, and heavily Si doped AlInGaN well 4985. An exemplary combination of doping and component distribution is shown in fig. 26A, which has the energy band diagram shown in fig. 26B.

The AlGaN layer 4981, in contact with or as the last layer of the heterostructure 40 or other suitable p-type AlGaN structure, has a higher Al composition to ensure transparency to UV emission generated by the MQW 30. For example, the Al composition and thickness of layer 4981 may be in the range of 0.5-0.65 and 2.0-5.0nm, respectively. AlGaN layer 4981 may be p-doped, such as Mg-doped, at a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 . Potential barrier 4982 has a higher Al composition than layer 4981, for exampleE.g., 0.1-0.5 above layer 4981. Alternatively, the barrier 4982 is a thin Mg doped AlN layer. The potential well 4983 has a smaller Al composition or no Al composition, e.g., 0.0-0.4, or alternatively no Al composition but has an In composition. It is desirable to have a large compositional discontinuity at the interface of the potential barrier 4982 and the potential well 4983 so that a high density of negative sheet charges is generated therein (s-a shown in fig. 26A and 26B _T2 ). The high density of interfacial sheet charge serves to sharply slope down the band edge of potential well 4983. For this reason, sigma is preferred according to the invention _T2 ≥3×10 ¹³ e·cm ^-2 I.e. -sigma _T2 ≤-3×10 ¹³ e·cm ^-2 . If the potential barrier 4982 and the potential well 4983 are made of AlGaN, this requires that the Al composition difference of the potential barrier 4982 and the potential well 4983 be equal to or greater than 0.6 (refer to equation 8).

The barrier 4894 also needs to have a high Al composition, optionally made of Mg doped AlN. The potential well 4985 has little or no Al composition, e.g., 0.0-0.4, or alternatively no Al composition but has an In composition. It is desirable to have a large compositional discontinuity at the interface of the potential barrier 4984 and the potential well 4985 so that a high density of negative sheet charges is generated therein (s-a shown in fig. 26A and 26B _T1 ). The high density of interfacial sheet charge serves to sharply slope down the band edge of potential well 4985. For this reason, sigma is preferred according to the invention _T1 ≥3×10 ¹³ e·cm ^-2 I.e. -sigma _T1 ≤-3×10 ¹³ e·cm ^-2 . If the potential barrier 4984 and the potential well 4985 are made of AlGaN, this requires that the Al composition difference of the potential barrier 4984 and the potential well 4985 be equal to or greater than 0.6 (refer to equation 8).

By removing Al component from

potential wells

4983 and 4985 and adding In component thereto, an interface thin layer (σ) of high density charge can be obtained according to fig. 5B, 5C, 6B and 6C _T1 ,σ _T2 ＞＞3×10 ¹³ e·cm ^-2 ). In this regard, the

barriers

4982 and 4984 are preferably made of thin Mg doped AlN, and the

potential wells

4983 and 4985 are preferably made of thin GaN or InGaN (e.g., in composition 0.1-0.3). The thicknesses of the

barriers

4982 and 4984 are in the range of 0.26-2.0nm, respectively, and the thicknesses of the

potential wells

4983 and 4985 are 0.5, respectively In the range of 2-3.0 nm. The thicknesses of the

barriers

4982 and 4984 may be the same or different. The thicknesses of

potential wells

4983 and 4985 may be the same or different. The ultra-thin film characteristics of the

barriers

4982, 4984 and

potential wells

4983, 4985 provide good vertical conductivity for carriers injected from the p-contact 62 and high UV transparency for photons generated from the MQW30. Further, potential well 4983 may be heavily Mg doped at 5.0x10 ¹⁹ -3.0×10 ²⁰ cm ^-3 Within a range of 1.0X10 and potential well 4985 may be heavily Si doped ¹⁹ -1.5×10 ²⁰ cm ^-3 Within a range of (2). The

barriers

4982 and 4984 may be Mg doped with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 。

The high density interfacial sheet charge will sharply slope down the band edges of narrow bandgap

potential wells

4983 and 4985, changing

potential wells

4983 and 4985 to p, respectively ⁺ A layer due to hole accumulation and becomes n ⁺ A layer due to electron accumulation. Due to p thus formed ⁺ Layers (4983) and n ⁺ The layers (4985) are in close proximity to each other (separated by only one thin AlN layer (4984)) and electrons in the valence band of the potential well 4983 are in a lower energy state in the conduction band of the potential well 4985 (see fig. 26B), so electrons in the valence band of the potential well 4983 can tunnel to the conduction band of the potential well 4985 when there is a positive bias on the potential well 4985. Extraction of electrons from the valence band of potential well 4983 is the same as injection of holes into the valence band of potential well 4983. That is, the p-type contact layer heterostructure 498 forms a tunneling junction to provide carrier injection from the p-ohmic contact 61 to the p-type AlGaN heterostructure 40, and hence to the MQW30.

Since potential well 4985 is n ⁺ The layer, due to the accumulation of electrons on the surface, can be selected from a large group of metals for fabricating the p-ohmic contact 61. In one embodiment, the p-ohmic contact 61 may be made of thin Ti/Al/Ti/Au, each having a layer thickness of 3-40/70-80/10-20/80-100nm, e.g., 3.5/75/15/90nm. In another embodiment, the p-ohmic contacts 61 may be made of V/Al/V/Au, each having a layer thickness of 3-80/70-150/10-50/20-800nm, e.g., 4.0/100/20/60nm (as with the n-ohmic contact 51, this needs to be stated). Such as nickel (Ni), tungstenHigh work function metals such as (W), palladium (Pd), platinum (Pt), iridium (Ir), osmium (Os), rhodium (Rh), and molybdenum (Mo) may also be used for p-ohmic contacts. In one embodiment, the p-ohmic contacts 61 are made of Ni/Rh with respective layer thicknesses of 3-10/30-150nm. The use of Al and Rd in the p-ohmic contact 61 enhances UV reflectivity and thus has better light extraction efficiency.

The invention has been described using exemplary embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and similar arrangements or equivalents which may be obtained by those skilled in the art without undue effort or undue experimentation. The scope of the claims is, therefore, to be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and equivalents.

Furthermore, a third aspect of the present invention provides:

item 1. A multiple quantum well structure for a light emitting device or photodetector comprising an AlGaN potential barrier and an AlGaN potential well alternately stacked, wherein the thickness of each of the AlGaN potential barrier and the AlGaN potential well satisfies:

wherein h is _i Is the thickness of the ith AlGaN barrier or potential well; sigma (sigma) _i Is the sheet charge density of the charge sheet on the surface of the ith AlGaN barrier or well that is oppositely charged relative to the net active dopant in the ith AlGaN barrier or well; ρ is _0i ＝eN _Di -eN _Ai Is the maximum bulk charge density, allowed by the applied doping concentration, in the depletion region of the ith AlGaN barrier or potential well created by the charge sheet, N _Di And N _Ai The donor and acceptor concentrations in the ith AlGaN barrier or well, respectively, and e is the fundamental charge level.

The multiple quantum well structure of item 2, item 1, wherein one or more of the AlGaN potential wells comprises an n-type doped AlGaN front well spacer, an n-type doped AlGaN back well spacer, and an AlGaN main potential well sandwiched between the n-type doped AlGaN front well spacer and the n-type doped AlGaN back well spacer, wherein an Al composition of the n-type doped AlGaN front well spacer and an Al composition of the n-type doped AlGaN back well spacer are different from an Al composition of the AlGaN main potential well, and a thickness of the n-type doped AlGaN front well spacer and a thickness of the n-type doped AlGaN back well spacer are less than a thickness of the AlGaN main potential well and a thickness of an adjacent AlGaN barrier.

The multiple quantum well structure of item 3, item 2, wherein the n-type doped AlGaN front well spacer and the n-type doped AlGaN back well spacer are Si doped with a doping concentration of 1.0 x 10, respectively ¹⁸ -8.0×10 ¹⁸ cm ^-3 The AlGaN main potential well is undoped or doped with Si, and the doping concentration is less than 5.0X10 ¹⁷ cm ^-3 At least one of the AlGaN barriers is doped with Si at a doping concentration of 1.0X10 ¹⁸ -8.0×10 ¹⁸ cm ^-3 。

The multiple quantum well structure of item 4, item 2, wherein the thickness of the n-type doped AlGaN front well spacer and the thickness of the n-type doped AlGaN back well spacer are respectively in a range of 0.1nm to 0.52 nm.

Item 5. The multiple quantum well structure of item 2, wherein the Al composition of the n-type doped AlGaN front well spacer layer and the Al composition of the n-type doped AlGaN back well spacer layer are higher than the Al composition of the adjacent AlGaN barrier.

The multiple quantum well structure of item 6, item 5, wherein the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are made of AlN and have thicknesses in the range of 0.1 to 0.52nm, respectively.

Item 7. The multiple quantum well structure of item 2, wherein the Al composition of the n-type doped AlGaN front well spacer and the Al composition of the n-type doped AlGaN back well spacer are lower than the Al composition of the AlGaN main potential well.

The multiple quantum well structure of item 8. Item 7, wherein the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer are made of GaN and have thicknesses in the range of 0.1 to 0.52nm, respectively.

The multiple quantum well structure of item 9, wherein the Al composition of the n-doped front well spacer is higher than the Al composition of the adjacent AlGaN barrier and the Al composition of the n-doped AlGaN back well spacer is lower than the Al composition of the AlGaN main potential well; or the Al component of the n-type doped AlGaN back well isolation layer is higher than the Al component of the AlGaN barrier, and the Al component of the AlGaN front well isolation layer is lower than the Al component of the AlGaN main potential well.

The multiple quantum well structure of item 9, wherein one of the n-type doped AlGaN front well isolation layer and the n-type doped AlGaN back well isolation layer is made of AlN and the other is made of GaN, and the thicknesses are respectively in the range of 0.1 to 0.52 nm.

Item 11. The multiple quantum well structure of item 2 further comprising an undoped AlGaN barrier formed on one side of the AlGaN potential well and in contact with the p-type structure of the light emitting device or photodetector on the other side.

The multiple quantum well structure of item 1, wherein one or more of the AlGaN barriers comprises one or more thin layers of positive charge and a distance between two adjacent thin layers of positive charge is greater than a depletion depth of a depletion region generated by any one of the two adjacent thin layers of positive charge.

Item 13 the multiple quantum well structure of item 12 wherein a positively charged thin layer is formed via Si delta-doping having a thin layer doping density of 10 or greater ¹² cm ^-2 。

The multiple quantum well structure of item 14, item 12, wherein each AlGaN barrier comprising a thin layer of positive charges comprises a dopant concentration of 1.0-8.0X10 ¹⁸ cm ^-3 Is separated by a thin layer of positive charge.

The multiple quantum well structure of item 15. Item 14, wherein the thickness of the Si doped layer of each AlGaN barrier containing a thin layer of positive charges is in the range of 6-10nm, respectively, and the thickness of the undoped layer of each AlGaN barrier containing a thin layer of positive charges is in the range of 2-4nm, respectively.

The multiple quantum well structure of item 12 further comprising an undoped AlGaN barrier formed on one side of the AlGaN potential well and in contact with the p-type structure of the light emitting device or photodetector on the other side.

The multiple quantum well structure of item 17, item 12, wherein one or more of the AlGaN potential wells comprises an n-type doped AlGaN front well spacer, an n-type doped AlGaN back well spacer, and an AlGaN main potential well sandwiched between the n-type doped AlGaN front well spacer and the n-type doped AlGaN back well spacer, wherein an Al composition of the n-type doped AlGaN front well spacer and an Al composition of the n-type doped AlGaN back well spacer are different from an Al composition of the AlGaN main potential well, and a thickness of the n-type doped AlGaN front well spacer and a thickness of the n-type doped AlGaN back well spacer are less than a thickness of the AlGaN main potential well and a thickness of an adjacent AlGaN barrier.

The multiple quantum well structure of item 18, item 17, wherein the n-type doped AlGaN front well spacer and the n-type doped AlGaN back well spacer are Si doped at a doping concentration of 1.0 x 10, respectively ¹⁸ -8.0×10 ¹⁸ cm ^-3 The AlGaN main potential well is undoped or doped with Si, and the doping concentration is less than 5.0X10 ¹⁷ cm ^-3 At least one of the AlGaN barriers is doped with Si at a doping concentration of 1.0X10 ¹⁸ -8.0×10 ¹⁸ cm ^-3 。

The multiple quantum well structure of item 19, wherein the thickness of the n-type doped AlGaN front well spacer and the thickness of the n-type doped AlGaN back well spacer are each in a range of 0.1nm to 0.52 nm.

The multiple quantum well structure of item 20. Item 17, wherein the Al composition of the n-type doped AlGaN front well spacer layer and the Al composition of the n-type doped AlGaN back well spacer layer are higher than the Al composition of the adjacent AlGaN barrier.

The multiple quantum well structure of item 21, wherein the Al composition of the n-doped AlGaN front well spacer and the Al composition of the n-doped AlGaN back well spacer are lower than the Al composition of the AlGaN main potential well.

Item 22. The multiple quantum well structure of item 17 wherein the Al composition of the n-doped front well spacer is higher than the Al composition of the adjacent AlGaN barrier and the Al composition of the n-doped AlGaN back well spacer is lower than the Al composition of the AlGaN main potential well; or the Al component of the n-type doped AlGaN back well isolation layer is higher than the Al component of the AlGaN barrier, and the Al component of the AlGaN front well isolation layer is lower than the Al component of the AlGaN main potential well.

Item 23. A light emitting diode comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the active region comprises the multiple quantum well structure of item 1.

A fourth aspect of the invention provides:

item 1. Heterostructures for light emitting devices or photodetectors comprising alternately stacked n-doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w N-well, wherein, N-type doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w The thickness of each of the N-wells satisfies the following:

Item 2. The heterostructure of item 1, wherein the n-type doped Al _b Ga _1-b N barrier and N-doped Al _w Ga _1-w The N-well is doped with Si at a doping concentration of 8.0X10 ¹⁸ –2.0×10 ¹⁹ cm ^-3 And b-w is equal to or greater than 0.15.

Item 3. The heterostructure of item 2, wherein the n-type doped Al _b Ga _1-b One or more of the N barriers comprises a Si delta-doped region.

Item 4. The heterostructure of item 1, wherein Al is doped in at least one n-type respectively _b Ga _1-b An N-type doped AlGaN front barrier isolation layer and an N-type doped AlGaN rear barrier isolation layer are formed on two sides of the N barrier, wherein the Al component of the N-type doped AlGaN front barrier isolation layer and the Al component of the N-type doped AlGaN rear barrier isolation layer are different from at least one N-type doped Al _b Ga _1-b Al component of N barrier, and thickness of N-type doped AlGaN front barrier isolation layer and N-type dopingThe thickness of the hetero AlGaN back barrier isolation layer is smaller than that of the at least one n-type doped Al _b Ga _1-b The thickness of the N barrier.

The heterostructure of item 5. Item 4, wherein the thickness of the n-type doped AlGaN front barrier spacer and the thickness of the n-type doped AlGaN back barrier spacer are in the range of 0.1nm to 1.5 nm.

The heterostructure of item 6, item 4, wherein the Al composition of the n-doped AlGaN front barrier layer and the Al composition of the AlGaN back barrier layer are higher than the at least one n-doped Al _b Ga _1-b The Al component of the N barrier.

Item 7. The heterostructure of item 4, wherein the Al composition of the AlGaN front barrier spacer and the Al composition of the AlGaN back barrier spacer are less than the adjacent n-doped Al _w Ga _1-w The Al composition of the N-well is low.

The heterostructure of item 8, item 4, wherein the Al composition of the AlGaN front barrier layer is higher than the at least one n-doped Al _b Ga _1-b The Al component of the N potential barrier and the Al component of the AlGaN back potential barrier isolation layer is lower than that of the adjacent N-type doped Al _w Ga _1- _w Al component of N potential well; or the Al component of the AlGaN back barrier isolation layer is higher than that of the at least one n-type doped Al _b Ga _1-b The Al component of the N potential barrier and the Al component of the AlGaN front barrier isolation layer is lower than that of the adjacent N-type doped Al _w Ga _1-w Al composition of the N-well.

Item 9. A light emitting device, comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the n-type AlGaN structure comprises the heterostructure of item 1.

The light emitting device of item 9, wherein the p-type AlGaN structure comprises a p-type heterostructure comprising one or more p-type doped AlGaN layers, each of the one or more p-type doped AlGaN layers comprising one or more positively charged thin layers interposed therebetween, wherein a distance between two adjacent positively charged thin layers is greater than a depletion depth of a depletion region generated by any one of the two adjacent positively charged thin layers.

The light emitting device of item 11, wherein the depletion depth of the depletion region generated by any one of the one or more thin layers of positive charge is less than 10nm.

The light-emitting device of item 10, wherein the one or more positively charged thin layers are formed by Si delta doping with a thin layer doping density of 1X 10 ¹¹ –1×10 ¹³ cm ^-2 。

The light emitting device of item 10, wherein the p-doped AlGaN layer disposed closest to the active region of the light emitting device or photodetector comprises a greater number of positively charged thin layers, a higher Al composition, and a greater thickness than the remaining layers of the one or more p-doped AlGaN layers.

The light emitting device of item 14, wherein the p-type heterostructure further comprises a plurality of p-doped AlGaN layers including no positively charged thin layers therein, alternately stacked with the one or more p-doped AlGaN layers including one or more positively charged thin layers, wherein an Al composition of each of the plurality of p-doped AlGaN layers including no positively charged thin layers therein is higher than an Al composition of an adjacent p-doped AlGaN layer including one or more positively charged thin layers, or an Al composition of each of the plurality of p-doped AlGaN layers including no positively charged thin layers therein is lower than an Al composition of an adjacent p-doped AlGaN layer including one or more positively charged thin layers.

The light emitting device of item 15, wherein the thin layer of positive charge divides each of the one or more p-doped AlGaN layers comprising the one or more thin layers of positive charge into a thinner front region and a thicker back region.

The light emitting device of item 16, wherein the p-type heterostructure further includes another p-type doped AlGaN layer, the one or more p-type doped AlGaN layers formed thereon, wherein the Al composition of the other p-type doped AlGaN layer is in the range of 0.6 to 0.8 and the thickness is in the range of 1.0 to 5.0 nm.

The light emitting device of item 17, wherein the p-type AlGaN structure comprises a p-type heterostructure comprising alternately stacked p-type doped AlGaN barriers and p-type doped AlGaN potential wells, wherein the thickness of each of the AlGaN barriers and AlGaN potential wells respectively satisfies:

wherein h is _i Is the thickness of the ith AlGaN barrier or potential well; sigma (sigma) _i Is the sheet charge density of the charge sheet on the surface of the ith AlGaN barrier or well that is oppositely charged relative to the net active dopant of the ith AlGaN barrier or well; ρ is _0i ＝eN _Di -eN _Ai Is the maximum bulk charge density allowed by the applied doping concentration, N in the depletion region of the ith AlGaN barrier or potential well created by the charge sheet _Di And N _Ai The donor and acceptor concentrations in the ith AlGaN barrier or well, respectively, e is the basic charge level; the method comprises the steps of,

wherein, at least one of the AlGaN potential barriers comprises an AlGaN front potential barrier isolation layer, an AlGaN rear potential barrier isolation layer and an AlGaN main potential barrier clamped between the AlGaN front potential barrier isolation layer and the AlGaN rear potential barrier isolation layer, wherein the Al component of the AlGaN front potential barrier isolation layer and the Al component of the AlGaN rear potential barrier isolation layer are different from the Al component of the AlGaN main potential barrier, and the thickness of the AlGaN front potential barrier isolation layer and the thickness of the AlGaN rear potential barrier isolation layer are smaller than the thickness of the AlGaN main potential barrier.

The light-emitting device of item 18, wherein the thickness of the AlGaN front barrier isolation layer and the thickness of the AlGaN back barrier isolation layer are in a range of 0.1nm to 1.5 nm.

The light-emitting device of item 19, wherein the Al composition of the AlGaN front barrier layer and the Al composition of the AlGaN rear barrier layer are higher than the Al composition of the AlGaN main barrier.

The light-emitting device of item 20. Item 19, wherein the AlGaN front barrier isolation layer and the AlGaN back barrier isolation layer are made of AlN and have thicknesses in the range of 0.26 to 0.52nm, respectively.

The light-emitting device of item 21, wherein the Al composition of the AlGaN front barrier layer and the Al composition of the AlGaN back barrier layer are lower than the Al composition of the adjacent AlGaN potential well.

The light-emitting device of item 22, item 21, wherein the AlGaN front barrier isolation layer and the AlGaN back barrier isolation layer are made of GaN and have thicknesses in the range of 0.1 to 0.52nm, respectively.

The light emitting device of item 23, wherein the Al composition of the AlGaN front barrier spacer is higher than the Al composition of the AlGaN main barrier and the Al composition of the AlGaN back barrier spacer is lower than the Al composition of the adjacent AlGaN potential well; or the Al component of the AlGaN back barrier isolation layer is higher than that of the AlGaN main barrier, and the Al component of the AlGaN front barrier isolation layer is lower than that of the adjacent AlGaN potential well.

The light emitting device of item 24, wherein the p-type heterostructure further comprises another p-type doped AlGaN barrier on which the alternately stacked p-type doped AlGaN barrier and the p-type doped AlGaN potential well are formed, wherein the other p-type doped AlGaN barrier comprises a main barrier in contact with a last quantum barrier of the MQW active region of the light emitting device or photodetector, and a back barrier isolation layer on which one of the alternately stacked p-type doped AlGaN barrier and the p-type doped AlGaN potential well is formed.

A fifth aspect of the invention provides:

item 1. A p-type heterostructure for a light emitting device or photodetector as a p-type contact layer, comprising:

a first potential barrier;

a first AlInGaN well formed on the first potential barrier;

a second AlInGaN well formed on the second AlGaN barrier;

The p-type contact layer of item 1, wherein at least one of the first AlGaN barrier and the second AlGaN barrier is made of AlN.

Item 3 the p-type contact layer of item 1, wherein at least one of the first AlInGaN well and the second AlInGaN well is formed of In _x Ga _1-x N, wherein x is equal to or less than 0.3.

The p-type contact layer of item 4, item 1, wherein the thickness of the first AlGaN barrier and the thickness of the second AlGaN barrier are each in the range of 0.26 to 2.0 nm.

The p-type contact layer of item 1, wherein the thickness of the first AlInGaN well and the thickness of the second AlInGaN well are each in the range of 0.52-3.0 nm.

The p-type contact layer of item 1, wherein the first AlInGaN well is doped p-type with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 And the second AlInGaN well is doped n-type with a doping concentration of 1.0X10 ¹⁹ –1.5×10 ²⁰ cm ^-3 。

The p-type contact layer of item 7, item 1, wherein the first AlGaN barrier is p-doped with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 And the second AlGaN barrier is doped p-type with a doping concentration of 5×10 ¹⁹ –3.0×10 ²⁰ cm ^-3 。

The p-type contact layer of item 8, further comprising an AlGaN layer on which the first AlGaN barrier is formed, wherein the AlGaN layer on which the first AlGaN barrier is formed has an Al composition lower than that of the first AlGaN barrier and in the range of 0.5-0.65, a thickness in the range of 2.0-5.0nm, and is p-type doped with a doping concentration of 5.0X10 ¹⁹ –3.0×10 ²⁰ cm ^-3 。

Item 9. A light emitting device, comprising:

an n-type AlGaN structure;

a p-type AlGaN structure;

a p-type contact mechanism formed on the p-type AlGaN structure, wherein the p-type contact mechanism comprises the p-type contact layer of item 1.

The light emitting device of item 10, wherein the p-doped AlGaN layer disposed closest to the active region of the light emitting device or photodetector comprises a greater number of positively charged thin layers, a higher Al composition, and a greater thickness than the other layers of the one or more p-doped AlGaN layers.

wherein h is _i Is the thickness of the ith AlGaN barrier or potential well; sigma (sigma) _i Is the sheet charge density of the charge sheet on the surface of the ith AlGaN barrier or well that is oppositely charged relative to the net active dopant of the ith AlGaN barrier or well; ρ is _0i ＝eN _Di -eN _Ai Is the maximum bulk charge density, allowed by the applied doping concentration, in the depletion region of the ith AlGaN barrier or potential well created by the charge sheet, N _Di And N _Ai The donor and acceptor concentrations in the ith AlGaN barrier or well, respectively, e is the basic charge level; the method comprises the steps of,

Claims

1. A heterostructure for a light emitting device or photodetector comprising one or more p-doped AlGaN layers, each of said one or more p-doped AlGaN layers comprising one or more positively charged lamellae interposed therebetween, wherein the distance between two adjacent positively charged lamellae is greater than the depletion depth of a depletion region generated by either of said two adjacent positively charged lamellae;

the heterostructure further includes: a plurality of p-type doped AlGaN layers having no thin layers of positive charges therein, alternately stacked with said one or more p-type doped AlGaN layers having one or more thin layers of positive charges; wherein the Al composition of each of the plurality of p-type doped AlGaN layers that do not include a thin layer of positive charge is higher than the Al composition of an adjacent p-type doped AlGaN layer that includes one or more thin layers of positive charge, or the Al composition of each of the plurality of p-type doped AlGaN layers that do not include a thin layer of positive charge is lower than the Al composition of an adjacent p-type doped AlGaN layer that includes one or more thin layers of positive charge.

2. The heterostructure of claim 1, wherein the depletion region created by any one of the one or more thin layers of positive charge has a depletion depth of less than 10nm.

3. The heterostructure of claim 1, wherein said one or more positively charged lamellae are formed by Si delta doping with a lamellae doping density of 1 x 10 ¹¹ –1×10 ¹³ cm ^-2 。

4. The heterostructure of claim 1, wherein the p-doped AlGaN layer disposed closest to the active region of the light emitting device or photodetector comprises a greater number of positively charged thin layers, a higher Al composition, and a greater thickness than the remaining layers of the one or more p-doped AlGaN layers.

5. The heterostructure of claim 1, wherein the thin layer of positive charge divides each of the one or more p-doped AlGaN layers comprising the one or more thin layers of positive charge into a thinner front region and a thicker back region.

6. The heterostructure of claim 1, further comprising: and another p-type doped AlGaN layer on which the one or more p-type doped AlGaN layers are formed, wherein the Al composition of the another p-type doped AlGaN layer is in the range of 0.6-0.8 and the thickness is in the range of 1.0-5.0 nm.

7. A heterostructure for a light emitting device or photodetector comprising alternately stacked p-type doped AlGaN barriers and p-type doped AlGaN potential wells, wherein the thickness of each of the AlGaN barriers and AlGaN potential wells respectively satisfies:

8. The heterostructure of claim 7, wherein at least one of the AlGaN barriers includes an AlGaN front barrier isolation layer, an AlGaN back barrier isolation layer, and an AlGaN main barrier sandwiched between the AlGaN front barrier isolation layer and the AlGaN back barrier isolation layer, wherein an Al composition of the AlGaN front barrier isolation layer and an Al composition of the AlGaN back barrier isolation layer are different from an Al composition of the AlGaN main barrier, and a thickness of the AlGaN front barrier isolation layer and a thickness of the AlGaN back barrier isolation layer are less than a thickness of the AlGaN main barrier.

9. The heterostructure of claim 8, wherein the AlGaN front barrier spacer and AlGaN back barrier spacer have a thickness in a range of 0.1nm to 1.5 nm.

10. The heterostructure of claim 8, wherein the Al composition of the AlGaN front barrier spacer and the Al composition of the AlGaN back barrier spacer are higher than the Al composition of the AlGaN main barrier.

11. The heterostructure of claim 10, wherein the AlGaN front and back barrier spacers are made of AlN and each have a thickness in the range of 0.26-0.52 nm.

12. The heterostructure of claim 8, wherein the Al composition of the AlGaN front barrier layer and the Al composition of the AlGaN back barrier layer are lower than the Al composition of an adjacent AlGaN potential well.

13. The heterostructure of claim 12, wherein the AlGaN front and back barrier spacers are made of GaN and each have a thickness in the range of 0.1-0.52 nm.

14. The heterostructure of claim 8, wherein the Al composition of the AlGaN front barrier spacer is higher than the Al composition of the AlGaN main barrier and the Al composition of the AlGaN back barrier spacer is lower than the Al composition of the adjacent AlGaN potential well; or the Al component of the AlGaN back barrier isolation layer is higher than that of the AlGaN main barrier, and the Al component of the AlGaN front barrier isolation layer is lower than that of the adjacent AlGaN potential well.

15. The heterostructure of claim 8, further comprising: the alternately stacked p-type doped AlGaN potential barrier and another p-type doped AlGaN potential barrier on which a p-type doped AlGaN potential well is formed, wherein the other p-type doped AlGaN potential barrier comprises: a main barrier in contact with the last quantum barrier of the MQW active region of the light-emitting device or photodetector, and a back barrier isolation layer on which one of the alternately stacked p-type doped AlGaN barrier and p-type doped AlGaN potential well is formed.

16. A light emitting device, comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the p-type AlGaN structure comprises the heterostructure of claim 1.

17. A light emitting device, comprising:

an n-type AlGaN structure;

a p-type AlGaN structure; the method comprises the steps of,

wherein the p-type AlGaN structure comprises the heterostructure of claim 7.