Source: https://patents.google.com/patent/JP2008543089A/en
Timestamp: 2020-01-18 07:05:58
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Matched Legal Cases: ['§119', 'Application No. 10', 'Application No. 60', 'Application No. 11', 'Application No. 60', 'Application No. 60', 'art 400', 'Application No. 60']

JP2008543089A - Method and apparatus for growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures and devices - Google Patents
Method and apparatus for growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures and devices Download PDF
JP2008543089A
JP2008543089A JP2008514810A JP2008514810A JP2008543089A JP 2008543089 A JP2008543089 A JP 2008543089A JP 2008514810 A JP2008514810 A JP 2008514810A JP 2008514810 A JP2008514810 A JP 2008514810A JP 2008543089 A JP2008543089 A JP 2008543089A
JP2008514810A
JP5743127B2 (en
2005-06-01 Priority to US68624405P priority Critical
2005-06-01 Priority to US60/686,244 priority
2006-06-01 Application filed by ザ リージェンツ オブ ザ ユニバーシティ オブ カリフォルニアＴｈｅ Ｒｅｇｅｎｔｓ ｏｆ Ｔｈｅ Ｕｎｉｖｅｒｓｉｔｙ ｏｆ Ｃａｌｉｆｏｒｎｉａ, 独立行政法人科学技術振興機構 filed Critical ザ リージェンツ オブ ザ ユニバーシティ オブ カリフォルニアＴｈｅ Ｒｅｇｅｎｔｓ ｏｆ Ｔｈｅ Ｕｎｉｖｅｒｓｉｔｙ ｏｆ Ｃａｌｉｆｏｒｎｉａ
2006-06-01 Priority to PCT/US2006/021128 priority patent/WO2006130696A2/en
2008-11-27 Publication of JP2008543089A publication Critical patent/JP2008543089A/en
2015-07-01 Publication of JP5743127B2 publication Critical patent/JP5743127B2/en
Identifying desired material properties for a particular device application; selecting a semipolar growth orientation based on said desired material properties; and selecting an appropriate substrate for growth of the selected semipolar growth orientation Growing a flat semipolar (Ga, Al, In, B) N template or nucleation layer on the substrate; and the flat semipolar (Ga, Al, In, B) N template Or a semipolar (Ga, Al, In, B) N thin film, a heterostructure with a step of growing a semipolar (Ga, Al, In, B) N thin film, heterostructure or device on the nucleation layer, and Methods for device growth and fabrication are provided. By using the above method, a semipolar (Ga, Al, In, B) N thin film, a heterostructure, and a device having a large area parallel to the substrate surface can be realized.
CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on 35 USC §119 (e), claims the benefit of provisional application of co-pending assignee of the following, which is assigned to the present invention.
Robert M. Robert M. Farrell, Troy J. Baker (Troy J. Baker), Apan Chakraborty, Benjamin A. Benjamin A. Haskell, P.M. P. Morgan Patison, Rajat Sharma, Umesh K. Uesh K. Misra, Stephen P. Denver (Steven P. DenBaars), James S. Spec (James S. Speck) and application 60 / 686,244 by Shuji Nakamura, filed Jun. 1, 2005, entitled "Semipolar (Ga, Al, In, B) N thin film, heterostructure and Method and apparatus for device growth and fabrication (TECHNIQUE FOR THE GROWTH AND FABRICATION OF SEMIPOLAR (Ga, Al, In, B) N THIN FILMS, HETEROSTRUCTURES, AND DEVICES) "Attorney Docket No. 30794.140 US-P1 2005-668).
This application is a related application of the following co-pending applications assigned to the assignee of the present invention.
Michael D. Craven (Michael D. Craven), Stacia Keller, Steven P. Denver, Tal Margarith, James S. Spec, Shuji Nakamura, Umesh K. US Patent Application No. 10 / 413,690 by Michela, filed Apr. 15, 2003, entitled “Nonpolar (Al, B, In, Ga) N Quantum Wells and Heterostructured Materials and Devices (NON-POLAR) (Al, B, In, Ga) N QUANTUM WELL AND HETEROSTUCTURE MATERIALS AND DEVICES) ", agent serial number 30794.101-US-U1 (2002-301). The above application claims the priority of the following patent document based on US Patent 119 (e).
Michael D. Craven, Stacia Keller, Steven P. Denver, Tal Margaris, James S. Spec, Shuji Nakamura, Umesh K. US Patent Provisional Application No. 60 / 372,909 by Michela, filed on Apr. 15, 2002, entitled "NON-POLAL GALLIUM NITRIDE BASED THIN FILMS AND HETEROSTURTURE MATERIALS" ) ", Agent reference number 30794.95-US-P1.
Arpan Chakraborty, Benjamin A. Haskell, Stacia Keller, James S. Spec, Stephen P. Denver, Shuji Nakamura, Umesh K. US Practical Application No. 11 / 123,805 by Michela, filed May 6, 2005, entitled "Non-polar Indium Gallium Nitride Thin Films, Heterostructures, and Devices by Metalorganic Chemical Vapor Deposition ( FABRICATION OF NONPOLAR INDIUM GALLIUM NITRIDE THIN FILMS, HETEROSTUCTURES AND DEVICES BY METALORGANIC CHEMICAL VAPOR DEPOSITION ”, agent number 30951. The above application claims the benefit of the following patent document under US Patent 119 (e).
Arpan Chakraborty, Benjamin A. Haskell, Stacia Keller, James S. Spec, Stephen P. Denvers, Shuji Nakamura, Umesh K. US Patent Provisional Application No. 60 / 569,749 by Michela, filed on May 10, 2004, entitled “Nonpolar InGaN Thin Films, Heterostructures and Devices by Metalorganic Chemical Vapor Deposition” (FABRICATION OF NONPOLAR InGaN THIN FILMS, HETEROSTRUCTURES AND DEVICES BY METALORGANIC CHEMICAL VAPOR DEPOSITION) ”, agent serial number 30794.117-US-P1, and Troy J. Baker, Benjamin A. Haskell, Paul T. Paul T. Fini, Stephen P. Denver, James S. Spec, and US Patent Provisional Application No. 60 / 660,283 by Shuji Nakamura, filed on Mar. 10, 2005, entitled “TECHNIQUE FOR THE GROWTH OF PLANAR SEMI-POLLAR GALLIUM” NITRIDE) ", agent reference number 30794.128-US-P1 (2005-471).
1. TECHNICAL FIELD OF THE INVENTION The present invention relates to semiconductor materials, methods, and devices, and more particularly to semipolar (Ga, Al, In, B) N thin films, heterostructures, and device growth and fabrication. It is.
2. Description of Related Art (Note: Throughout this specification, this application refers to a number of different publications, indicated by one or more reference numbers in parentheses, eg, [reference x]. (A list of these documents listed below is provided in the section labeled [References] below, each of which is incorporated herein by reference.)
The usefulness of gallium nitride (GaN) and its alloys (Ga, Al, In, B) N has been well established in the fabrication of visible and ultraviolet optoelectronic devices and high power electronic devices. As shown in FIG. 1, state-of-the-art nitride thin films, heterostructures and devices are grown along the [0001] axis 102 of the wurtzite nitride crystal structure 100. Such total polarization of the thin film consists of a spontaneous polarization component and a piezoelectric polarization component, both of which originate from the only polar [0001] axis 102 of the wurtzite nitride crystal structure 100. When the nitride heterostructure is grown to be pseudomorphic, polarization discontinuities are formed at the crystal surface and interface. This discontinuity causes carriers to accumulate or decrease at the surface and interface and generate an electric field. Since the direction of this built-in electric field coincides with the normal growth direction [0001] of nitride thin films and heterostructures, this electric field has the effect of tilting the energy band of the nitride device.
In the c-plane wurtzite (Ga, Al, In, B) N quantum well, the inclined energy bands 104 and 106 divide the hole wave function 108 and the electron wave function 110 into a space, as shown in FIG. Separate. This spatial charge separation reduces the oscillator strength of the radiative transition and redshifts the emission wavelength. These effects are manifestations of the quantum confined Stark effect (QCSE) and have been well analyzed for nitride quantum wells [references 1-4]. Furthermore, large polarization-induced electric fields may be partially shielded by dopants and injected carriers [Refs. 5 and 6], thus making it difficult to accurately design emission characteristics.
Furthermore, it is shown that the biaxial strain that matches the pseudo lattice has little influence on the reduction of the effective mass of holes in the c-plane wurtzite (Ga, Al, In, B) N quantum well [references]. 7]. This is in stark contrast to conventional III-V zinc blende InP- and GaAs-based quantum wells, where the latter causes heavy hole bands and light holes induced by anisotropic strain. Band separation results in a significant reduction in the effective mass of holes. For conventional III-V zinc blende InP- and GaAs-based quantum wells, the reduction of the effective mass of holes significantly increases the quasi-Fermi level for a given carrier density. As a direct consequence of this increased quasi-Fermi level separation, the carrier density required to generate optical gain is significantly reduced [Ref. 8]. However, in the wurtzite nitride crystal structure, in the c-plane nitride quantum well subjected to biaxial strain, because of the hexagonal symmetry and the spin-orbit interaction in the nitrogen atom is small, The separation of the generated heavy and light hole bands is very small [Ref. 7]. Thus, in a c-plane nitride quantum well subjected to biaxial strain, the effective mass of holes remains much larger than the effective mass of electrons, and the carriers required to generate optical gain. The density is very high.
In (Ga, Al, In, B) N devices, one way to remove the effects of polarization and reduce the effective mass of holes is to grow the device on the nonpolar face of the crystal. These planes include {11-20} planes collectively referred to as a-planes and {1-100} planes collectively referred to as m-planes. Such planes contain the same number of gallium and nitrogen atoms in the plane and are charge neutral. As a result, the different nonpolar layers are equivalent to each other, and the bulk crystal does not polarize along the growth direction. Furthermore, it has been shown that a strained nonpolar InGaN quantum well has a significantly smaller effective mass of holes than a strained c-plane InGaN quantum well [Ref 9]. However, despite the progress made by the University of California and other researchers [Refs. 10-15], the growth and fabrication of nonpolar (Ga, Al, In, B) N devices still remains challenging. It has not yet been widely adopted in the nitride industry.
Another way to reduce the effects of polarization in (Ga, Al, In, B) N devices and reduce the effective mass of holes is to grow the device on the semipolar plane of the crystal. The term “semipolar plane” is used to refer to a plane that cannot be classified as a c-plane, a-plane, or m-plane. In crystallographic terms, a semipolar surface is any surface that has at least two non-zero Miller indices h, i, or k and a non-zero Miller index l.
The growth of semipolar (Ga, Al, In, B) N thin films and heterostructures was demonstrated on the sidewalls on the c-plane oriented stripe pattern. Nishizuka et al. [Ref 16] grew {11-22} InGaN quantum wells in this manner. However, this method of fabricating semipolar nitride thin films or heterostructures is an epitaxial lateral overgloss (ELO) artifact and is clearly different from the disclosure of the present invention. In this method, the semipolar crystal plane is not parallel to the substrate surface, and the available surface area is too small to be processed into a semipolar device.
The present invention provides semipolar (Ga, Al, In, B) on a suitable substrate or flat (Ga, Al, In, B) N template so that the large area of the semipolar thin film is parallel to the substrate surface. N thin films, heterostructures, and methods for growing and making devices are described. In contrast to the growth of micrometer-sized ramps previously tested as semipolar nitrides, this method uses semi-lithographic techniques to produce semipolar (Ga, Al, In, B) N devices. Can be produced on a large scale.
Compared with sphalerite InP- and GaAs-based quantum well heterostructures and devices, wurtzite c-plane (Ga, Al, In, B) N quantum well heterostructures and devices generate optical gain. A high carrier density is required. This is due to the presence of a large polarization-induced electric field and the essentially large effective mass of holes [Refs. 17, 18]. Therefore, the reduction of the built-in electric field and the effective mass of holes is essential for the realization of high performance (Ga, Al, In, B) N devices.
Typical InP and GaAs based heterostructure device designs typically include various thin film parameters such as composition, thickness and strain. Changing these parameters can change electronic and optical properties such as the band gap, dielectric constant, and effective mass of holes of each epitaxial layer. Although not normally used in the design of InP- and GaAs-based devices, changing the crystal growth orientation can also affect the electronic and optical properties of each epitaxial layer. In particular, changing the crystal growth orientation can reduce the influence of polarization and the effective mass of holes in nitride thin films and heterostructures. To include this new design parameter, we have invented methods of growing and fabricating semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices. By appropriately selecting the correct substrate or semipolar template for crystal growth, the optimal combination of net polarization and effective hole mass can be selected that is suitable for individual device applications.
In order to show the effect of changing the crystal growth orientation, the piezoelectric polarization is calculated for the In x Ga 1-x N quantum well subjected to compressive strain, and the angle between the general growth direction and the c-axis Can be plotted as a function of [Refs. 9, 18-20]. FIG. 2 shows the relationship between the conventional coordinate system (x, y, z) for c-plane crystal growth and the new coordinate system (x ′, y ′, z ′) for general crystal growth orientation. The conventional coordinate system (x, y, z) can be transformed into a new coordinate system (x ′, y ′, z ′) using the following rotation matrix.
Here, φ and θ are respectively an azimuth angle and a polar angle with respect to the [0001] axis of the new coordinate system. As shown in FIG. 2, the z-axis corresponds to the [0001] axis 102, and the z′-axis 200 corresponds to a new general crystal growth axis. Since the piezoelectric effect in the wurtzite type material is uniaxial isotropic along the [0001] axis, the dependence on the azimuth angle (φ) 202 can be ignored in the calculation of physical parameters [Reference 21]. In this way, a family of equivalent semipolar planes can be uniquely represented using a single polar angle (θ) 204. Hereinafter, θ is simply referred to as a crystal angle 204. The crystal angles 204 of polar, nonpolar, and some selected semipolar planes are shown in Table 1 below.
Table 1: Table of crystal angles corresponding to polar, nonpolar, and some selected semipolar planes
As expected, the {0001} plane corresponds to θ = 0 °, the {1-100} and {11-20} planes correspond to θ = 90 °, and the semipolar plane satisfies 0 ° <θ <90 °. Correspond.
The piezoelectric polarization of the crystal is determined by the strain state of the crystal. For heteroepitaxial growth of crystal layers that are not lattice matched, the strain state of each layer is determined by biaxial stress on the growth surface.
For a general crystal growth orientation along the z ′ axis 200, the biaxial stress components σ x′x ′ and σ y′y ′ in the growth plane are converted to the normal (x, y, z) can be converted to a coordinate system. As a result, the strain state and piezoelectric polarization in the (x, y, z) coordinate system can be determined. Thus, the piezoelectric polarization in the (x, y, z) coordinate system changes as a function of the crystal angle (θ) 204 via the transformation matrix U. For general crystal growth orientation, piezoelectric polarization is obtained by taking the scalar product of the polarization vector P in the (x, y, z) coordinate system and the unit vector z ′ along the general crystal growth direction. be able to.
Here, P x and P z represent piezoelectric polarization components in the (x, y, z) coordinate system, and depend on the crystal angle (θ) 204 as described above.
FIG. 3 shows a piezoelectric polarization 300 as a function of the angle between the growth direction and the c-axis for an In x Ga 1-x N quantum well with a strain-free GaN barrier layer and subjected to compressive strain [reference Reference 9, 18-20]. As expected, polarization 300 is maximum for c-plane growth (θ = 0 °) and zero for a-plane or m-plane growth (θ = 90 °). In the middle between these two points, the polarization changes once and becomes zero at a certain angle θ 0 302. The exact value of θ 0 302 depends on the values of some physical parameters, such as piezoelectric tensors and elastic constants, which are mostly unknown at present [References 21-25].
Similar to the piezoelectric polarization effect, the effective mass of holes in the compressive strain In x Ga 1-x N quantum well can be greatly reduced by changing the crystal growth orientation. Theoretical study results [Reference 9] show that the effective mass of holes in the compressive strain In x Ga 1-x N quantum well is crystallized by the separation of heavy and light hole bands induced by anisotropic strain. It shows a monotonous decrease with increasing angle. Thus, growing the compressive strained In x Ga 1-x N quantum well in a semipolar orientation, particularly in an orientation with a large crystal angle, will greatly reduce the effective mass of holes.
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The present invention describes methods of growing and fabricating semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices. These structures are grown directly on a suitable substrate or on a semipolar (Ga, Al, In, B) N template layer previously deposited on the substrate. Vapor phase epitaxial growth methods such as metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE) are used to grow semipolar (Ga, Al, In, B) N structures. However, the present invention is equally applicable to growth of semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices by molecular beam epitaxy (MBE) or other suitable growth techniques.
Semipolar nitride thin film and heterostructure growth techniques provide a means for reducing the effects of polarization and the effective mass of holes in wurtzite nitride device structures. The term nitride has the molecular formula of (Ga w Al x In y B z ) N with 0 ≦ w ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, and w + x + y + z = 1. It refers to all alloy compositions of (Ga, Al, In, B) N semiconductors. Currently marketed nitride devices are grown along the polar [0001] c-direction. The resulting polarization-induced electric field and the effective mass of large holes have a fatal effect on the properties of optoelectronic devices using nitrides of current technology.
Growing these devices along the semipolar direction could significantly improve device characteristics by reducing the built-in electric field and the effective mass of holes. Reducing the built-in electric field will reduce the spatial charge separation in the nitride quantum well. Similarly, reducing the effective mass of holes will reduce the carrier density required to generate optical gain in nitride laser diodes.
Hereinafter, with reference to the drawings, the same reference numerals are given to corresponding parts throughout.
In the following description of the preferred embodiments, reference is made to the accompanying drawings. The accompanying drawings are presented to illustrate certain embodiments in which the invention may be practiced. It should be noted that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
SUMMARY The present invention is configured to include semi-polar (Ga, Al, In, B ) N thin films, heterostructures, and devices of growth and the manufacturing methods. The flowchart 400 of FIG. 4 summarizes the key steps in the growth of semipolar (Ga, Al, In, B) N thin films and heterostructures.
Steps 402 and 404 outline the top-down device design procedure used to select the semipolar growth orientation. First, as shown in step 402, the desired material properties (piezoelectric polarization, effective mass of holes, etc.) for a particular device application must be determined. Based on these desired properties, in order to grow a heterostructure with a semipolar (Ga, Al, In, B) N thin film, a semipolar orientation with an optimal combination of material properties must be selected in step 404. I must. This top-down device design procedure is of course idealized. That is, it is assumed that the crystal quality is the same for all semipolar orientations. Adjustments in the device design procedure are made to match the execution process.
After selecting the optimal semipolar growth orientation, an appropriate substrate must be selected at step 406. Ideally, the substrate is a free-standing semipolar nitride wafer having a composition that is lattice matched to the structure to be grown. However, the substrate is often made of a dissimilar material such as MgAl 2 O 4 (spinel) or Al 2 O 3 (sapphire). In some cases, the heterogeneous substrate is coated with a nitride template layer, which can be HVPE, MOCVD, MBE, liquid phase epitaxy (LPE), chemical beam epitaxy (CBE) plasma enhanced chemical vapor deposition ( PECVD), sublimation, or sputtering, but is not limited to this, and all suitable growth techniques are used to form the film. The composition of the template layer need not exactly match the composition of the structure to be deposited. The thickness of the template layer ranges from a few nanometers (in this case called the nucleation layer or buffer layer) to tens or hundreds of micrometers. A template layer is not absolutely necessary, but using a template generally improves uniformity and improves the yield of semipolar nitride devices. In the following part of the description of this technical disclosure, the case of using an HVPE grown semipolar GaN template for the implementation of the present invention is described, but is not intended to limit the technical scope of the present invention and is intended to be exemplary.
Once the substrate or template is selected, in step 408 it is loaded into the reactor to prepare for the growth of the desired semipolar (Ga, Al, In, B) N thin film and heterostructure. For the practice of the present invention, suitable growth methods used in steps 410-418 include, but are not limited to, HVPE, MOCVD, MBE, LPE, CBE, PECVD, sublimation, sputtering, or any other vapor deposition method. Is not to be done. For illustrative purposes, the following part of the description of this technical disclosure describes the growth of semipolar thin films and heterostructures by MOCVD. However, focusing on this method does not limit the application of the present invention to other growth techniques. Finally, when a semipolar (Ga, Al, In, B) N structure is grown, the crystal is removed from the thin film growth reactor and processed into a semipolar device at step 420.
Technical Description The present invention describing the growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices includes the following elements.
1. Identify the desired material properties for a particular device application.
2. Select a semipolar orientation with the best combination of material properties.
3. Selecting an appropriate substrate or template for the growth of the desired semipolar orientation.
4). Growing semipolar thin films, heterostructures, and devices using suitable growth techniques.
As mentioned above, the significance of carrying out the present invention is emphasized by using a thick flat semipolar GaN template grown in HVPE. To date, several types of flat semipolar GaN template orientations have been successfully grown by the HVPE method. Details of template growth are disclosed separately. See the following literature.
Troy J. Baker, Troy J. Baker, Benjamin Benjamin A. Haskell, Paul T. Paul T. Fini, Stephen P. Denver (Steven P. DenBaars), James S. Spec (James S. Speck) and US Patent Provisional Application No. 60 / 660,283 by Shuji Nakamura, filed on Mar. 10, 2005, entitled “Flat Semi-polar Gallium Nitride Growth Technology ( TECHNIQUE FOR THE GROWTH OF PLANAR SEMI-POLAR GALLIUM NITRIDE) ", proxy number 30794.128-US-P1 (2005-471). This application is incorporated herein by reference.
In summary, the following four examples of flat semipolar nitride templates have been experimentally shown.
1. {10-11} GaN on {100} spinel miscut in the specified direction.
2. {10-13} GaN on {110} spinel.
3. {11-22} GaN on {1-100} sapphire.
4). {10-13} GaN on {1-100} sapphire.
The quality of these semipolar crystals is almost independent of growth temperature and pressure. The {10-11} and {10-13} orientations grew at pressures between 10 Torr and 1,000 Torr and temperatures between 900 ° C. and 1200 ° C., but there was little difference in overall crystal quality. . This wide range of pressure and temperature indicates that these semipolar planes are very stable when grown on a particular substrate. The epitaxial relationship between a specific substrate and a specific semipolar plane is true regardless of the type of growth system used to make the thin film. However, the optimum reactor conditions for growing these planes will vary depending on the individual reactor design and growth method.
Using these flat HVPE grown semipolar GaN layers as templates to grow semipolar (Ga, Al, In, B) N thin films and heterostructures using MOCVD, on several different semipolar orientations A semipolar (Ga, Al, In, B) NLED was grown and fabricated. In particular, on the {10-11} GaN template on {100} spinel, on the {10-13} GaN template on {1-100} sapphire, and on the {10-13} GaN template on {110} spinel A semipolar LED has been successfully demonstrated experimentally.
As shown in FIG. 5, the semipolar LED structure as the first example was regrown by MOCVD on a 10 μm thick HVPE grown {10-11} GaN template 502 on a {100} spinel substrate 504. The regrowth performed using the vertical MOCVD reactor began with the growth of a 2.0 μm thick Si-doped, n-type GaN base layer 506. The active region 508 is formed of a multi-quantum well (MQW) having a thickness of 16 nm and a five-cycle multi-quantum well (MQW) in which an Si-doped GaN barrier layer and a thickness of 4 nm are stacked. A 16 nm thick, undoped GaN barrier layer 510 is deposited at a low temperature to cap the InGaN MQW structure and prevent InGaN from evaporating and dissociating from the active region in the latter half of the growth. Next, a 300 nm thick Mg-doped p-type GaN layer 512 is formed. This structure is capped with a 40 nm thick, Mg highly doped p + -type GaN contact layer 514.
Following growth, a 300 × 300 μm 2 diode mesa is cut with chlorine-based reactive ion etching (RIE). Pd / Au (20/200 nm) and Al / Au (20/200 nm) were used as the p-type GaN and n-type GaN electrodes 516 and 518, respectively. A schematic cross section of a semipolar LED structure and a {10-11} plane 520 is shown in FIG. The electrical and light emission characteristics of the diode were measured using on-wafer inspection means of the device. A typical LED current-voltage (IV) characteristic 600 is shown in FIG. The relative optical power measured under direct current (dc) conditions was measured using a calibrated large area Si photodiode for light emitted to the back surface through the spinel substrate. The LED's electroluminescence (EL) spectrum and output power are measured as a function of drive current and are shown in FIGS. 7 and 8, respectively. All measurements were performed at room temperature.
As shown in FIG. 6, the IV characteristic 600 of the diode has a series resistance of 6.9Ω, and exhibits a low turn-on voltage of 3.1V. The EL spectrum was also measured at a drive current in the range of 30 to 200 mA. As shown in FIG. 7, the device exhibits an emission spectrum 700-710 in the blue spectral region of 439 nm for all drive currents and no peak shift is observed. The emission spectra 700-710 correspond to driving currents of 30 mA-200 mA, respectively. The fact that no blue shift occurs in the emission peak even when the drive current is increased is to be contrasted with the normal blue shift phenomenon observed in c-plane LEDs operating in the same drive current region in this wavelength region. .
Finally, output power on the wafer and external quantum efficiency were measured as a function of dc drive current. As shown in FIG. 8, the output power 800 increased almost linearly as the drive current increased from 10 mA to 300 mA. When the forward current was 20 mA, the output power was 11 μW, and the corresponding external quantum efficiency (EQE) 802 was 0.02%. It was measured when a DC power of 630 μW was a driving current of 300 mA. As the drive current increased, the EQE increased and reached a maximum value of 0.081% at 200 mA, where the forward current increased beyond 200 mA and decreased slightly. The fact that the EQE does not significantly decrease with the increase in the drive current is to be contrasted with the phenomenon in which a large decrease in EQE usually observed in c-plane LEDs operating in the same drive current region in this wavelength region occurs. is there.
Although not shown here, {0001} GaN on {0001} sapphire mounted together with a blue (˜439 nm peak) semipolar LED grown on a {10-11} GaN template on {100} spinel. Photoluminescence (PL) spectra were compared for c-plane LEDs grown on the template. “Mounted together” means that the c-plane template is mounted on the MOCVD reactor at the same time as the semipolar template, meaning that the two templates are mounted on the same support during the growth period. . The PL spectrum of the semipolar LED was very similar to the PL spectrum of the c-plane LED mounted together. This means that the semi-polar In x Ga 1-x N thin film and the c-plane In x Ga 1-x N thin film have the same indium uptake efficiency. This result indicates that there is a strong uptake of impurities along the semipolar plane and is consistent with previous research on lateral epitaxial overgloss along the semipolar plane [Refs. 26, 27].
In addition to the blue (˜439 nm peak) LED grown on the {10-11} GaN template on {100} spinel, FIG. 9 shows on the {10-13} GaN template 902 on the {1-100} sapphire substrate 904. Shows a green (˜525 nm peak) LED 900 grown. This semipolar LED structure 900 is regrowth using MOCVD on a 10 μm thick HVPE grown {10-13} GaN template 902 on {1-100} sapphire 904. The regrowth was performed in a conventional MOCVD reactor with a horizontal gas flow, starting with the growth of a 500 nm thick, Si-doped, n-type GaN base layer 906. The active region 908 is formed of a multiple quantum well (MQW) in which five cycles of an undoped GaN barrier layer and an InGaN quantum well of 4 nm thickness are stacked for 8 periods. A 20 nm thick, Mg-doped, p-type AlGaN barrier layer 910 is deposited at a low temperature, thereby capping the InGaN MQW structure and preventing InGaN from evaporating and dissociating from the active region 908 in the latter half of the growth. . This structure is capped with Mg-doped p-type GaN 912 having a thickness of 200 nm.
After growth, a 300 × 300 μm 2 diode mesa is cut out by chlorine-based RIE. Pd / Au (5/6 nm) and Ti / Al / Ni / Au (20/100/20/300 nm) were used as the p-type GaN and n-type GaN electrodes 914 and 916, respectively. FIG. 9 shows a schematic cross section of a semipolar LED structure and a {10-13} plane 918. The electrical and light emission characteristics of the diode were measured using on-wafer inspection means of the device. A typical LED current-voltage (IV) characteristic 1000 is shown in FIG. The relative light power measured under direct current (dc) conditions was measured using a calibrated large area Si photodiode for light emitted to the back surface through the sapphire substrate. The LED's electroluminescence (EL) spectrum and output power are measured as a function of drive current and are shown in FIGS. 11 and 12, respectively. All measurements were performed at room temperature.
As shown in FIG. 10, the IV characteristic 1000 of the diode has a series resistance of 14.3Ω and a low turn-on voltage of 3.2V. The EL spectrum was also measured at a drive current in the range of 30 to 200 mA. As shown in FIG. 11, the EL spectrum 1100 shows that the device 900 emits in the green spectral region with a slight peak shift from 528 nm at 20 mA to 522 nm at 200 mA. The fact that a large blue shift does not occur in the emission peak even when the drive current is increased should be contrasted with the fact that a large blue shift phenomenon is usually observed in c-plane LEDs operating in the same drive current region in this wavelength region. It is.
The on-wafer output power and external quantum efficiency were also measured as a function of dc drive current. As shown in FIG. 12, the output power 1200 increased almost linearly as the drive current increased from 10 mA to 250 mA. The output power 1200 when the forward current was 20 mA was 19.3 μW, and the corresponding external quantum efficiency (EQE) 1202 was 0.041%. It was measured when a DC power of 264 μW was a driving current of 250 mA. The EQE 1202 increased as the drive current increased, reaching a maximum value of 0.052% at 120 mA, and decreased slightly as the forward current increased beyond 120 mA. The fact that the EQE 1202 does not significantly decrease with the increase of the drive current is to be contrasted with the phenomenon that the EQE 1202 that is normally observed in the c-plane LED operating in this wavelength region operates in the same drive current region. is there.
Finally, FIG. 13 shows a blue (˜440 nm peak) semipolar LED 1300 regrowth on a {10-13} GaN template 1302 on a {110} spinel substrate 1304. In the regrowth performed using the vertical MOCVD reactor, an Si-doped, n-type GaN base layer 1306 having a thickness of 2.0 μm was first grown. The active region 1308 is composed of a multi-quantum well (MQW) having a thickness of 16 nm and a Si-doped GaN barrier layer and a thickness of 4 nm, and a 5-period multi-quantum well (MQW) layered. A 16 nm thick, undoped GaN barrier layer 1310 is deposited at a low temperature, thereby capping the InGaN MQW structure and preventing InGaN from evaporating and dissociating from the active region 1308 in the latter half of the growth. Next, a 300 nm thick Mg-doped p-type GaN layer 1312 is formed. This structure is capped with a 40 nm thick, highly Mg doped, p + -type GaN contact layer 1314.
Following growth, a 300 × 300 μm 2 diode mesa is cut with chlorine-based RIE. Pd / Au (20/200 nm) and Al / Au (20/200 nm) were used as the p-type GaN and n-type GaN electrodes 1316 and 1318, respectively. A schematic cross section of a semipolar LED structure and a {10-13} plane 1320 is shown in FIG. The electrical and light emission characteristics of the diode were measured using on-wafer inspection means of the device. The relative optical power measured under direct current (dc) conditions was measured using a calibrated large area Si photodiode for light emitted to the back surface through the spinel substrate. Although not shown here, the EL spectrum as a function of IV characteristics and drive current is similar to a blue (˜439 nm peak) semipolar LED grown on a {10-11} GaN template on {100} spinel. Met. The emitted light output of the LED is measured as a function of drive current and is shown in FIG. All measurements were performed at room temperature.
As shown in FIG. 14, the output power 1400 increased almost linearly when the drive current increased from 10 mA to 90 mA, and then increased sub-linearly to 250 mA. The output power 1400 at a forward current of 20 mA was 190 μW, and the corresponding external quantum efficiency (EQE) 1402 was 0.34%. A high DC output of 1.53 mW was measured at a drive current of 250 mA. The EQE 1402 increases with an increase in driving current, takes a maximum value of 0.41% at 50 mA, and then greatly decreases when the forward current increases beyond 50 mA. As the drive current increases in this way, the EQE 1402 greatly decreases due to the semipolar LED grown on the {10-11} GaN template on the {100} spinel (˜439 nm peak) and the {1-100} sapphire. Contrast this with EQE1402 in green (˜525 nm) semipolar LEDs grown on the {10-13} GaN template. However, compared to these other two semipolar LEDs, this semipolar LED shows significantly higher peak output power 1400 and peak EQE1402 values, which is clearly possible in competition with c-plane nitride technology Is shown.
The device structure described above constitutes the first report of working semipolar InGaN-based LEDs. In summary, the present invention has demonstrated semipolar LEDs operating on two different semipolar orientations, on three different substrates, and in two different spectral regions. These are blue (~ 439 nm peak) semipolar LED grown on {10-11} GaN template on {100} spinel, green grown on {10-13} GaN template on {1-100} sapphire. It includes (˜525 nm) semipolar LEDs and blue (˜440 nm peak) semipolar LEDs grown on {10-13} GaN templates on {100} spinel. These three examples are for illustrative purposes only and should not be construed as limiting the possibility of applying the invention to other growth orientations or device structures.
Possible changes and transformations
The device described in the technical description section included a light emitting diode. However, the scope of the present invention includes the growth and fabrication of any semipolar (Ga, Al, In, B) N device. Therefore, the device structure is not limited to LEDs. Other possible semipolar devices that can be grown and fabricated using the method of the present invention are edge emitting laser diodes (EEL), vertical cavity surface emitting laser diodes (VCSEL), and LEDs with resonators ( RCLED), microresonator LED (MCLED), high electron mobility transistor (HEMT), heterojunction bipolar transistor (HBT), heterojunction field effect transistor (HFET), and visible, ultraviolet, and near ultraviolet photodetectors Yes. Furthermore, these examples and other possibilities possess all of the advantages of semipolar (Ga, Al, In, B) N devices. This list of possible devices is for illustrative purposes only and is not a limitation on the application of the present invention. Rather, the present invention includes all nitride-based devices grown along or on the semipolar plane.
In particular, the present invention can provide significant advantages in the design and fabrication of (Ga, Al, In, B) N laser diodes. Such advantages are particularly important in long wavelength laser diodes with particularly large piezoelectric fields, such as the conceptual device 1500 as shown in FIG. Furthermore, as the theoretical calculation shows, the effective mass of holes for compressive strained In x Ga 1-x N quantum wells due to the separation of heavy and light hole bands induced by anisotropic strain. Decreases monotonically as the crystal angle increases [Ref. 9]. The calculation results of self-consistent multibody optical gain for compressively strained In x Ga 1-x N quantum wells show that the peak gain is very sensitive to the effective mass of holes, and this gain increases monotonically with increasing crystal angle This suggests [References 17 and 18]. Thus, the high carrier density required to generate optical gain in a conventional nitride-based laser diode is due to the laser structure on the semipolar orientation, particularly on the orientation with a crystal angle close to θ = 90 °. It can be reduced by growing.
This is reflected in the design of the laser diode 1500 shown in FIG. Among the semipolar orientations we have experimentally shown, the {10-11} orientation 1501 has the largest crystal angle (θ = 62.0 °) and provides the greatest optical gain improvement. A {10-11} semipolar GaN template 1504 is grown using a {100} spinel substrate 1502, where the n-GaN layer 1506 is regrown as described above. Next, an n-AlGaN / GaN cladding layer 1508 is grown, and an n-GaN waveguide layer 1510 is grown thereon. Next, an MQW active layer 1512 is grown, and a p-GaN waveguide layer 1514 is grown on the MQW active layer 1512. Therefore, another cladding layer 1516 is grown and a p-GaN contact layer is grown. A Ni / Au electrode 1520 and a Ti / Al / Ni / Au electrode 1522 are formed.
The present invention also provides gains in the characteristics of electronic devices. The reduced effective mass of holes in the strained semipolar (Ga, Al, In, B) N layer leads to an increase in hole mobility, which leads to a semipolar p-type (Ga, Al, In, B). ) N layer conductivity increases. Greater mobility in strained semipolar p-type (Ga, Al, In, B) N layers leads to improved characteristics of bipolar electronic devices such as HBTs. Further, when the p-type conductivity in the semipolar nitride increases, the series resistance of the pn junction diode and the LED decreases. Furthermore, by changing the crystal growth orientation, the magnitude and direction of piezoelectric polarization can be adapted to the particular device application. Thus, devices that utilize piezoelectric polarization to create the desired properties of the device (such as HEMT) will benefit from the versatile invention.
Variations in semipolar (Ga, Al, In, B) N quantum wells and heterostructures are possible without departing from the scope of the present invention. Furthermore, in addition to the number of quantum wells grown, the intrinsic thickness and composition of the layers can be varied depending on the particular device design and may be used in other embodiments of the invention. For example, the device in the preferred embodiment of the present invention utilizes InGaN-based quantum wells for light emission in the blue and green spectral regions. However, the scope of the present invention also includes devices with AlGaN-, AlInN-, and AlInGaN-based quantum wells, which can be incorporated into designs for light emission in other spectral regions. Furthermore, future devices such as semipolar HEMTs, HBTs, and HFETs may not include quantum wells in their device structures.
Variations in MOCVD growth conditions such as growth temperature, growth pressure, V / III ratio, precursor flow rate and source material are also possible without departing from the scope of the present invention. Interface quality control is an important aspect of the process and is directly related to the flow switching capability of a particular reactor design. Continued efforts to optimize growth conditions lead to more precise control of the composition and thickness of the semipolar thin films and heterostructures described above.
It is possible to incorporate other impurities or dopants into the semipolar nitride thin film, heterostructure, or device described in this invention. For example, Fe, Mg, and Si are doped into various layers in a nitride heterostructure, which are often added to modify the conduction properties of this layer and adjacent layers. It is within the scope of the present invention to use such dopants and other dopants not listed here.
In a preferred embodiment, the method includes first growing a semipolar template by HVPE and then growing semipolar (Ga, Al, In, B) N thin films and heterostructures by MOCVD. However, other growth methods and procedures may be used in other embodiments of the invention. Other possible growth methods include HVPE, MOCVD, MBE, LPE, CBE, PECVD, sublimation and sputtering. The flow chart shown in FIG. 4 provides a generalized example to show how many growth methods and procedures are used to implement the present invention.
The technical scope of the present invention includes other than the four semipolar GaN template orientations described in the preferred embodiment. The idea of the present invention relates to all (Ga, Al, In, B) N compositions on all semipolar orientations. For example, {10-11} AlN, InN, AlGaN, InGaN, AlInN, or AlGaInN can be grown on a miscut (100) spinel substrate. Similarly, {20-21} templates can be grown if a suitable substrate is found. Furthermore, these examples and other possibilities enjoy all the benefits of flat semipolar thin films.
The present invention also includes selection of specific crystal terminations and polarities. Braces {} used throughout this specification indicate a family of symmetrical equivalent planes. Therefore, the {10-12} family includes (10-12), (-1012), (1-102), (-1102), (01-12), and (0-112) planes. All of these faces are terminated with group III atoms. This means that the c-axis of the crystal is oriented away from the substrate. This family of faces also includes a corresponding nitrogen termination face with the same index. In other words, the {10-12} family is (10-1-2), (-101-2), (1-10-2), (-110-2), (01-1-2), and It also includes the (0-11-2) plane. For each of these growth orientations, the c-axis of the crystal is oriented toward the substrate. Although the choice of polarity affects the behavior of the lateral growth process, all aspects within a single crystallographic family are equivalent for the purposes of the present invention. In some applications, it is desirable to grow on a nitrogen-terminated semipolar surface, and in other cases, growth on a Group III-terminated surface is preferred. The termination of the semipolar plane is greatly moved by substrate selection and pretreatment. Both terminations meet the operating conditions of the present invention.
Furthermore, substrates other than sapphire and spinel can be used for the growth of semipolar templates. The scope of the present invention includes the growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices on all possible crystallographic orientations of all possible substrates. Such substrates share silicon carbide, gallium nitride, silicon, zinc oxide, boron nitride, lithium aluminate, lithium niobate, germanium, aluminum nitride, lithium gallate, partially substituted spinel, and γ-LiAlO 2 structure Including, but not limited to, quaternary tetrahedral oxides.
Furthermore, changing the semipolar (Ga, Al, In, B) N nucleation layer (or buffer layer) and the nucleation layer growth method satisfies the conditions for implementing the present invention. The growth temperature, growth pressure, orientation, and composition of the nucleation layer need not match the growth temperature, growth pressure, orientation, and composition of the subsequent semipolar thin film and heterostructure. The scope of the present invention is to use all possible nucleation layers and nucleation layer growth methods to produce semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices on all possible substrates. Growing and making.
The semipolar (Ga, Al, In, B) N device described above was grown on a flat semipolar GaN template. However, the scope of the present invention also includes semipolar (Ga, Al, In, B) N devices grown on semipolar epitaxial lateral overgloss (ELO) templates. The ELO technique is a method for reducing the density of threading dislocations (TD) in the subsequent epitaxial layer. Reducing the TD density improves the device characteristics. For LEDs, these improvements include increased internal quantum efficiency and reduced reverse leakage current. For laser diodes, these improvements include increased output power, increased internal quantum efficiency, extended device lifetime, and reduced threshold current density [Ref 28]. These advantages relate to all semipolar flat thin films, heterostructures, and devices grown on semipolar ELO templates.
The above and other embodiments were considerations for semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices grown on heterogeneous substrates. Ideally, however, the substrate is a free-standing semipolar nitride wafer with a composition that is lattice matched to the structure to be grown. Free-standing semipolar nitride wafers can be obtained by removing dissimilar substrates from thick semipolar nitride layers, or by cutting bulk nitride ingots or balls into individual semipolar nitride wafers, or other possible crystalline Can be made by growth or wafer manufacturing techniques. The scope of the present invention covers semipolar (Ga, Al, In, B) N thin films on all possible free-standing semipolar nitride wafers made using all possible crystal growth methods and wafer fabrication techniques. , Heterostructures, and device growth and fabrication.
One or more embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the scope of the present invention. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.
Advantages and Improvements current art is to grow along the polar [0001] c-direction (Ga, Al, In, B ) the N thin films and heterostructures. The resulting effective mass of holes, which is large with the electric field induced by polarization, is fatal to the properties of the state-of-the-art nitride optoelectronic devices. The advantage of the present invention is that the growth of (Ga, Al, In, B) N thin films and heterostructures along the semipolar direction dramatically improves device characteristics by reducing the effects of polarization and the effective mass of holes. It can be improved. Prior to the present invention, there was no means for growing large area semipolar nitride thin films, heterostructures, or devices.
As an illustration of possible improvements to current technology, the device characteristics of our green (˜525 nm peak) semipolar LED grown on the {10-13} GaN template on the {1-100} sapphire described above are shown in c-plane. Compare with device characteristics of InGaN LED with typical commercial green spectral region (~ 525nm peak) grown on GaN template. The data presented below is collected from a standard commercial device encapsulated in a hemispherical epoxy dome. The total area of the active region was 300 × 300 μm 2 , which was the same as the area of the active region of our green semipolar LED.
The electrical characteristics and light emission characteristics of commercially available LEDs were measured by applying a bias to the device enclosed in the package. The IV characteristics of the LED are shown in FIG. The relative light output measured under direct current (dc) conditions was obtained by collecting the light from the top of the hemispherical epoxy dome onto a calibrated large area Si photodiode. The LED EL spectrum and emitted light output were also measured as a function of drive current. This data is shown in FIGS. 17 and 19, respectively. All measurements were performed at room temperature.
As shown in FIG. 16, the IV characteristic 1600 of a commercially available LED showed a turn-on voltage of 3.5 V and a series resistance of 28.9Ω. These values are large compared to the forward voltage and series resistance values of 3.1 V and 14.3 Ω, respectively, of our green semipolar LED. The most natural explanation is that the difference in turn-on voltage between the two LEDs can be attributed to the reduced polarization-induced electric field in the semipolar LED compared to the commercial LED. Due to the reduction of the built-in electric field, in the semipolar diode, a current can flow even if the separation of the n-type and p-type pseudo-Fermi levels is small, resulting in a low turn-on voltage.
As shown in FIG. 17, the EL spectrum 1700 of a commercially available LED was also measured at a drive current in the range of 20 mA to 100 mA. The EL peak shift as a function of drive current was compared between a commercial green LED and our green semipolar LED. As shown in FIG. 18, the wavelength graph 1800 of the commercially available device shifted from 523 nm at 20 mA to 511 nm at 100 mA over the entire wavelength of 12 nm in the current range of 80 mA. Compared to a commercially available device, the wavelength graph 1802 of the green semipolar LED shifted from 528 nm at a current of 20 mA to 522 nm at a current of 250 mA, with a current ranging from 230 mA over a total of 6 nm. In the semipolar LED, the blue shift of the emission peak decreases as the drive current increases. This is because the polarization-induced electric field in the active region is reduced in the semipolar LED compared to the commercially available LED.
Relative light output power and external quantum efficiency relative to commercial LEDs were also measured as a function of dc drive current. The light output was measured by collecting light emitted from the top of a hemispherical epoxy dome onto a calibrated large area Si photodiode. The use of such a power measurement method is intended to obtain a relative output power measurement as a function of drive current and is intended to measure the total output power emitted from a commercial LED. is not. As shown in FIG. 19, when the drive current increased from 10 mA to 130 mA, the output power 1900 increased in a sub-linear manner, and at 90 mA, an abnormal jump possibly due to a thermal effect was shown. At 110 mA, the output power saturates, and as the current increases, its magnitude decreases, and at 140 mA, the device eventually breaks due to thermal effects.
Unlike semipolar LEDs, the commercial LED EQE 1902 peaks at very low drive currents of 10 mA, and then quite low at high drive currents. As shown in FIG. 19, the EQE 1902 of a commercial LED decreases by 65.7% between currents of 10 mA and 130 mA. For comparison, as shown in FIG. 12, the EQE of a semipolar LED peaks at a relatively high drive current of 120 mA, and then decreases by only about 8% even if the drive current is increased beyond 120 mA. The fact that our semipolar LED does not show a significant decrease in EQE even when the drive current is increased is that a commercially available c-plane LED operating in the same drive current region in this wavelength band usually shows a significant decrease in EQE. Should be contrasted with The mechanism behind this rather large difference in the EQE-I characteristics of our semipolar LEDs and commercial LEDs is currently unknown, but the polarization-induced electric field of semipolar LEDs is reduced compared to commercial c-plane LEDs. It can be inferred that it is related to doing.
Finally, commercially available c-plane nitride LEDs do not show any polarization anisotropy in their electroluminescence. On the other hand, nonpolar m-plane nitride LEDs showed strong polarization anisotropy along the [0001] axis [Reference 15]. This polarization can be attributed to the anisotropic strain-induced separation of the heavy and light hole bands in the compressive strained m-plane In x Ga 1-x N quantum well. Similarly, with respect to the general crystal growth orientation, the anisotropic strain-induced separation of the heavy hole band and the light hole band is divided into an optical matrix element polarized in the x ′ direction and an optical matrix polarized in the y ′ direction. There is a major discrepancy between the elements [Ref 9]. Thus, the light emitted from the semipolar nitride optoelectronic device also exhibits strong polarization anisotropy.
The above discussion includes a comparison of semipolar (Ga, Al, In, B) N thin films, heterostructures and devices with commercially available c-plane (Ga, Al, In, B) N thin films, heterostructures and devices. Similar comparisons can be made between nonpolar (Ga, Al, In, B) N thin films, heterostructures and devices. Similar to semipolar thin films and heterostructures, nonpolar thin films and heterostructures can be used to improve device characteristics by reducing the effects of polarization and effective mass of holes. However, since it is very difficult to grow high quality nonpolar templates, thin films and heterostructures, nonpolar devices are not currently manufactured. One advantage of semipolar thin films and heterostructures over nonpolar thin films and heterostructures is the ease of crystal growth. The present invention discloses semipolar thin films and heterostructures that have a larger tolerance parameter space during growth than nonpolar thin films and heterostructures. For example, nonpolar thin films and heterostructures do not grow at atmospheric pressure, but semipolar thin films and heterostructures have been experimentally shown to grow from 62.5 Torr to 760 Torr, growing in a wider area. there's a possibility that. Thus, unlike nonpolar thin films and heterostructures, semipolar (Ga, Al, In, B) N thin films and heterostructures show relatively little correlation between growth pressure and crystal quality. Has been.
Another advantage of the semipolar surface over the nonpolar surface is improved indium uptake efficiency. Low indium incorporation efficiency in nonpolar a-plane In x Ga 1-x N thin films has been a significant problem when growing optoelectronic devices on a-plane GaN templates [Ref. 12]. As discussed above, our data suggest that the indium uptake efficiency in the semipolar In x Ga 1-x N thin film is equivalent to the indium uptake efficiency in the c-plane In x Ga 1-x N thin film. . As already demonstrated by the green (˜525 nm) LEDs grown on {10-13} GaN templates on our {1-100} sapphire, this high indium uptake efficiency is due to the semipolar In x Ga 1− a light emitting region of the LED of the x N helps extended to longer wavelengths.
The report recently disclosed by Nishika et al. [Ref. 16] on {11-22} InGaN quantum wells grown on patterned c-plane oriented stripe sidewalls is the closest comparison to our work. However, this method of fabricating semipolar thin films and heterostructures is a byproduct of epitaxial lateral overgrowth (ELO) and is significantly different from our disclosed technique. The semipolar crystal plane is not parallel to the substrate surface and the surface area available is too small to be processed into a semipolar device.
An advantage of the present invention is the growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures and devices on a suitable substrate or template where the large area of the semipolar thin film is parallel to the substrate surface. Including. In contrast to growth with a tilted surface at the micrometer dimensions previously exemplified as semipolar nitride, this method uses a large number of semipolar (Ga, Al, In, B) N devices using standard lithographic methods. Scale production is possible.
A new feature of the present invention is the establishment of the ability to grow and fabricate flat semipolar (Ga, Al, In, B) N thin films, heterostructures and devices. This has been experimentally confirmed by the authors for (Ga, Al, In, B) N devices grown on three different semipolar orientations. The advantages discussed previously apply to all flat semipolar nitride thin films, heterostructures and devices.
Process Diagram FIG . 20 shows a process diagram according to the present invention.
Box 2000 shows the process of selecting the semipolar growth orientation.
Box 2002 represents the step of selecting a substrate that fuses with the growth of the selected semipolar growth orientation.
Box 2004 represents the step of growing a flat semipolar (Ga, Al, In, B) N template layer on the surface of the substrate.
Box 2006 shows the process of growing a semipolar (Ga, Al, In, B) N thin film on a semipolar (Ga, Al, In, B) N template layer.
References The following references are incorporated herein by reference.
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Conclusion This concludes the description of the preferred embodiment of the present invention. One or more embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the scope of the present invention. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.
Is a diagram representing the band bending in the compressive strain ln x Ga 1-x N quantum wells due to the electric field of polarization-induced. It is a figure which shows the relationship between the normal coordinate system (x, y, z) with respect to the growth of a c-plane crystal | crystallization, and the conversion coordinate system (x ', y', z ') with respect to the general crystal growth orientation. The azimuth and polar angles are denoted by φ and θ, respectively. FIG. 6 shows piezoelectric polarization 300 as a function of the angle between the growth direction and the c-axis for an In x Ga 1-x N quantum well with a strain-free GaN barrier layer and subjected to compressive strain. 2 is a flowchart outlining the main steps of growth and fabrication of semipolar (Ga, Al, In, B) N thin films, heterostructures, and devices. This flow chart shows that many different growth methods and processes can be used within the scope of the present invention. 1 is a schematic cross-sectional view of a blue (−439 nm peak) LED grown on a {10-11} semipolar GaN template. FIG. It is a graph of the current-voltage (IV) characteristic of blue (-439 nm peak) LED grown on a {10-11} semipolar GaN template. It is a figure showing the electroluminescence (EL) spectrum in various drive currents of blue (-439 nm peak) LED grown on the {10-11} semipolar GaN template. FIG. 6 is a graph showing output power and external quantum efficiency (EQE) in a wafer state as a function of drive current in a blue (−439 nm peak) LED grown on a {10-11} semipolar GaN template. FIG. 10 is a schematic cross-sectional view of a green (−525 nm peak) LED grown on a {10-13} semipolar GaN template. It is a graph of the current-voltage (IV) characteristic of green (-525nm peak) LED grown on the {10-13} semipolar GaN template. FIG. 10 is a diagram representing electroluminescence (EL) spectra at various driving currents of a green (−525 nm peak) LED grown on a {10-13} semipolar GaN template. FIG. 6 is a graph showing output power and external quantum efficiency (EQE) in a wafer state as a function of drive current in a green (−525 nm peak) LED grown on a {10-13} semipolar GaN template. FIG. 6 is a schematic cross-sectional view of a blue (−440 nm peak) LED grown on a {10-13} semipolar GaN template. It is a graph showing the output power in a wafer state and external quantum efficiency (EQE) as a function of a drive current in blue (-440 nm peak) LED grown on a {10-13} semipolar GaN template. 1 is a schematic diagram of a semipolar nitride laser diode designed to emit in the green region of the spectrum (−525 nm peak). FIG. Among the illustrated semipolar orientations, the {10-11} semipolar orientation provides an optimal combination of net polarization and effective hole mass in the active region of the semipolar nitride laser. It is a graph of the current-voltage (IV) characteristic of the green (-525nm peak) commercial LED grown on the c-plane GaN template. It is a figure showing the electroluminescence (EL) spectrum in various drive currents of the green (-525nm peak) commercial LED grown on the c-plane GaN template. Peep wavelength of electroluminescence (EL) at various drive currents of green (-525 nm peak) LEDs grown on {10-13} semipolar GaN template and green (-525 nm peak) grown on c-plane GaN template It is a graph which compares with commercially available LED. It is a graph showing the output power after packaging and external quantum efficiency (EQE) as a function of drive current in a green (-525 nm peak) commercial LED grown on a c-plane GaN template. 4 is a process chart according to the present invention.
A method of growing and producing a semipolar (Ga, Al, In, B) N thin film,
(B) selecting a substrate that fuses with the growth of the selected semipolar growth orientation;
(C) growing a flat semipolar (Ga, Al, In, B) N template layer on the surface of the substrate; and (d) on the semipolar (Ga, Al, In, B) N template layer. And the step of growing the semipolar (Ga, Al, In, B) N thin film.
The selecting step (a) comprises identifying a desired material property for a particular device application, and selecting the semipolar growth orientation based on the desired material property. Item 2. The method according to Item 1.
The method of claim 1, wherein the substrate comprises a free-standing semipolar nitride wafer having a composition lattice matched to the semipolar (Ga, Al, In, B) N thin film.
The method of claim 1, wherein the substrate comprises a dissimilar material.
The method of claim 4, wherein the dissimilar material is coated with a nitride template layer.
The method of claim 1, wherein a large area of the semipolar (Ga, Al, In, B) N thin film is parallel to the surface of the substrate.
The method of claim 1, wherein the template layer is a nucleation layer.
The method of claim 1, wherein the semipolar (Ga, Al, In, B) N thin film is a heterostructure.
The method of claim 1, further comprising processing the semipolar (Ga, Al, In, B) N thin film into a device.
The method of claim 1, wherein the step of selecting a substrate includes reducing the effective mass of holes in the semipolar (Ga, Al, In, B) N thin film.
A device made using the method of claim 1.
(B) selecting a substrate that fuses with the growth of the selected semipolar growth orientation; and (c) growing the semipolar (Ga, Al, In, B) N thin film on the substrate. A method characterized by comprising.
The selecting step (a) comprises identifying a desired material property for a particular device application, and selecting the semipolar growth orientation based on the desired material property. Item 13. The method according to Item 12.
The method of claim 12, wherein the substrate comprises a free-standing semipolar nitride wafer having a composition lattice matched to the semipolar (Ga, Al, In, B) N thin film.
The method of claim 12, wherein the substrate comprises a dissimilar material.
The method of claim 15, wherein the dissimilar material is coated with a nitride template layer.
The method according to claim 12, characterized in that the large area of the semipolar (Ga, Al, In, B) N thin film is parallel to the surface of the substrate.
The method according to claim 12, further comprising processing the semipolar (Ga, Al, In, B) N thin film into a device.
The method of claim 12, wherein selecting the substrate comprises reducing the effective mass of holes in the semipolar (Ga, Al, In, B) N thin film.
A device made using the method of claim 12.
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