Patent Application
20230268721
In the decades since the original proposal of the ICL, a multitude of developments have paved the way for this III-V based technology to yield efficient and coherent mid-IR sources. Operating in a wide range of wavelengths from below 3 μm to above 11 μm, ICLs based on the type-II QW active region boast many technological applications including gas/chemical sensing, imaging, and industrial process control.
While type-II ICLs, grown mostly on GaSb substrates, have demonstrated efficient room temperature operation in the 3-6 μm range, two key questions remain: 1) Can the ICL support longer wavelength operation with low threshold current densities? and 2) Just how far into the longer-wavelength regime can the ICL technology be pushed? It should be noted that extension to longer wavelengths is challenging for the mature GaSb-based ICLs. This is primarily due to the InAs/AlSb SL needed to form the optical cladding layers. Such an SL would need to be significantly thicker to accommodate the longer optical wave decay length, which complicates the MBE growth. Additionally, the SL has a low thermal conductivity, so an increase in the overall SL thickness would cause the thermal resistance of the device to increase accordingly, hindering performance.
One solution to alleviate such concerns is to instead grow ICL structures on InAs substrates and replace the InAs/AlSb SL cladding with n+-doped InAs plasmon-enhanced cladding in combination with undoped InAs SCLs. This InAs-based approach enabled pulsed lasing up to 55° C. near 7.1 μm and extended the ICL operation to 11.1 μm, the longest wavelength at the time among III-V interband lasers. However, the Jth of the latter, long-wavelength device was relatively high (e.g., 95 A/cm2 at 80 K in CW mode near 10.8 μm) and operated only up to 97 and 130 K in CW and pulsed modes, respectively. This relatively modest device performance can be improved significantly by using an advanced waveguide configuration, which was later developed for InAs-based ICLs operating near 4.6 μm. By introducing an intermediate SL cladding layer between the SCL and the plasmon cladding layer, the advanced waveguide configuration can enhance the optical confinement and simultaneously reduce the optical loss, resulting in a low Jth. Although plasmon-enhanced waveguide ICLs can be achieved on GaSb substrates with heavily doped n+-InAsSb layers and GaSb SCLs, this occurs at the cost of more complicated carrier transport and MBE growth.
For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.
Disclosed herein are InAs-based ICLs with an advanced waveguide structure having improved device performance in terms of reduced threshold current densities for ICLs near 11 μm in a 7289 wafer, or extended operating wavelength beyond 13 μm in a 7342 wafer. In the 7289 wafer, ICLs near 11 μm yielded a significantly reduced CW lasing threshold of 23 A/cm2 at 80 K with substantially increased CW output power compared with previous ICLs at similar wavelengths. In the 7342 wafer, ICLs incorporated an innovative QW active region, comprised of InAsP layers, and lased in pulsed mode up to 120 K at 13.2 μm, the longest wavelength yet achieved for III-V interband lasers.
Before further describing various embodiments of the apparatus, component parts, and methods of the present disclosure in more detail by way of exemplary description, examples, and results, it is to be understood that the embodiments of the present disclosure are not limited in application to the details of apparatus, component parts, and methods as set forth in the following description. The embodiments of the apparatus, component parts, and methods of the present disclosure are capable of being practiced or carried out in various ways not explicitly described herein. As such, the language used herein is intended to be given the broadest possible scope and meaning; and the embodiments are meant to be exemplary, not exhaustive. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting unless otherwise indicated as so. Moreover, in the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to a person having ordinary skill in the art that the embodiments of the present disclosure may be practiced without these specific details. In other instances, features which are well known to persons of ordinary skill in the art have not been described in detail to avoid unnecessary complication of the description. While the apparatus, component parts, and methods of the present disclosure have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the apparatus, component parts, and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the inventive concepts as described herein. All such similar substitutes and modifications apparent to those having ordinary skill in the art are deemed to be within the spirit and scope of the inventive concepts as disclosed herein.
All patents, published patent applications, and non-patent publications referenced or mentioned in any portion of the present specification are indicative of the level of skill of those skilled in the art to which the present disclosure pertains, and are hereby expressly incorporated by reference in their entirety to the same extent as if the contents of each individual patent or publication was specifically and individually incorporated herein.
Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those having ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
As utilized in accordance with the methods and compositions of the present disclosure, the following terms and phrases, unless otherwise indicated, shall be understood to have the following meanings: The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or when the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” The use of the term “at least one” will be understood to include one as well as any quantity more than one, including but not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, or any integer inclusive therein. The phrase “at least one” may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100/1000 are not to be considered limiting, as higher limits may also produce satisfactory results. In addition, the use of the term “at least one of X, Y and Z” will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y and Z.
As used in this specification and claims, the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.
Throughout this application, the terms “about” or “approximately” are used to indicate that a value includes the inherent variation of error for the apparatus, composition, or the methods or the variation that exists among the objects, or study subjects. As used herein the qualifiers “about” or “approximately” are intended to include not only the exact value, amount, degree, orientation, or other qualified characteristic or value, but are intended to include some slight variations due to measuring error, manufacturing tolerances, stress exerted on various parts or components, observer error, wear and tear, and combinations thereof, for example. The terms “about” or “approximately”, where used herein when referring to a measurable value such as an amount, percentage, temporal duration, and the like, is meant to encompass, for example, variations of ±20% or ±10%, or ±5%, or ±1%, or ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods and as understood by persons having ordinary skill in the art. As used herein, the term “substantially” means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance occurs to a great extent or degree. For example, the term “substantially” means that the subsequently described event or circumstance occurs at least 90% of the time, or at least 95% of the time, or at least 98% of the time.
As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
As used herein, all numerical values or ranges include fractions of the values and integers within such ranges and fractions of the integers within such ranges unless the context clearly indicates otherwise. Thus, to illustrate, reference to a numerical range, such as 1-10 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., and so forth. Reference to a range of 1-50 therefore includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., up to and including 50, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., 2.1, 2.2, 2.3, 2.4, 2.5, etc., and so forth. Reference to a series of ranges includes ranges which combine the values of the boundaries of different ranges within the series. Thus, to illustrate reference to a series of ranges, for example, a range of 1-1,000 includes, for example, 1-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-75, 75-100, 100-150, 150-200, 200-250, 250-300, 300-400, 400-500, 500-750, 750-1,000, and includes ranges of 1-20, 10-50, 50-100, 100-500, and 500-1,000. The range 100 units to 2000 units therefore refers to and includes all values or ranges of values of the units, and fractions of the values of the units and integers within said range, including for example, but not limited to 100 units to 1000 units, 100 units to 500 units, 200 units to 1000 units, 300 units to 1500 units, 400 units to 2000 units, 500 units to 2000 units, 500 units to 1000 units, 250 units to 1750 units, 250 units to 1200 units, 750 units to 2000 units, 150 units to 1500 units, 100 units to 1250 units, and 800 units to 1200 units. Any two values within the range of about 100 units to about 2000 units therefore can be used to set the lower and upper boundaries of a range in accordance with the embodiments of the present disclosure. More particularly, a range of 10-12 units includes, for example, 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, and 12.0, and all values or ranges of values of the units, and fractions of the values of the units and integers within said range, and ranges which combine the values of the boundaries of different ranges within the series, e.g., 10.1 to 11.5.
The present disclosure will now be discussed in terms of several specific, non-limiting, examples and embodiments. The examples described below, which include particular embodiments, will serve to illustrate the practice of the present disclosure, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of particular embodiments and are presented in the cause of providing what is believed to be a useful and readily understood description of procedures as well as of the principles and conceptual aspects of the present disclosure.
The following abbreviations apply:
7289 and 7342 Wafers
Returning to the description of the various embodiments of the disclosure, herein are disclosed InAs-based ICLs with the advanced waveguide structure for long wavelength operation. Devices with a 7289 wafer showed significantly reduced threshold current densities compared to previous ICLs at similar wavelengths near 11 μm. Devices with a 7342 wafer extended the lasing wavelength of ICLs longer than 13 μm with an innovative QW active region comprised of InAsP layers based on the relevant perspective on band-edge positions in type-II heterostructures, which discussed a method to address the issue of a reduced wavefunction overlap for photon emission at long wavelengths with spatially indirect transitions in a type-II QW.
Two sets of 20-stage ICLs were grown on InAs substrates, both including the advanced waveguide design, where the layer thicknesses of the intermediate SL cladding and InAs SCL layers were 1.65 μm and 0.83 μm, respectively. The bottom n+-InAs plasmon cladding layer thickness was 2 μm, while the top was 1.1 μm. The doping level of the plasmon cladding was 3.2×1018 cm−2, which was lowered by approximately 54% compared with Lu Li, et al., “MBE-grown long-wavelength interband cascade lasers on InAs substrates,” Journal of Crystal Growth, 425, 369 (2015), which is incorporated by reference, to reduce optical losses due to free carrier absorption.
In addition to adapting the advanced waveguide for both ICLs, the 7342 wafer had a modified active region compared with the 7289 wafer in order to enhance its long wavelength operation. In the 7289 wafer, a typical AlSbAs/InAs/Ga0.65In0.35Sb/InAs/AlSbAs W-shape QW active region was employed with layer thicknesses of 23/34.5/28/31.5/12 Å in the growth direction. When extending operation to longer wavelengths, a thicker InAs layer may be needed, which leads to a reduced electron-hole wavefunction overlap in this type-II QW as the electrons and holes are mainly localized at different layers. This could cause the optical gain (generated from the spatially indirect interband transition in the type-II QW) to be insufficient to overcome the increased loss at a long wavelength and thus render the lasing unreachable. But as pointed out in R. Q. Yang, “Electronic States and Interband Tunneling Conditions in Type-II Quantum Well Heterostructures,” J. Appl. Phys. 127, 025705 (2020), which is incorporated by reference, the energy level of an electronic state in a QW could be moved down by using a barrier layer with a low valence band-edge, resulting in a lower interband transition energy for photon emission at longer wavelengths. Phosphorus-containing compounds are such a barrier material that can lower the electron energy level for longer wavelength emission without increasing the InAs layer thickness. So, for the 7342 wafer, a modified active region consisting of a AlSbAs/InAs0.5P0.5/InAs/Ga0.65In0.35Sb/InAs/InAs0.5P0.5 QW was grown, with layer thicknesses of 19/16/26.5/28/21.5/16 Å, respectively, where the InAs layer thicknesses were substantially reduced (e.g., 26.5 vs. 34.5 A) compared to that in the first ICL wafer. The band-edge diagram of one cascade stage along with the layer sequence for the 2nd ICL wafer is given in
The grown wafers were fabricated into 100-μm-wide (EB7289BA1-1A and EB7342BA1-3G devices) and 150-μm-wide (EB7289BA1-1E, EB7342BA1-3F, and EB7342BA1-3E devices) BA mesas using wet chemical etching. The wafers were left un-thinned and cleaved into 1.5-mm-long laser bars without facet coating, which were mounted epi-side up on copper heat sinks for testing.
Multiple EB7289 devices were able to operate in CW mode above 100 K, and in pulsed mode above 130 K with lasing wavelengths near 11 μm, as shown in
In CW mode, a representative device from the first ICL wafer, EB7289BA1-1A, lased at 10.2 μm at 80 K and operated up to 107 K at an emission wavelength of 10.65 μm as shown in the inset in
Under pulsed operation, EB7289BA1-1A was able to operate up to 137 K at a wavelength of 10.85 μm, as shown in the inset in
A representative device with the 7342 wafer, EB7342BA1-3G, lased at a wavelength of 12.7 μm in pulsed mode at 80 K, albeit with a large Jth of 179 A/cm2. The maximum operating temperature for this device was 115 K, at a lasing wavelength of 13.23 μm, which represents a new record for long wavelength operation among III-V interband lasers. Also, three more devices with the 7342 wafer, EB7342BA1-3E, EB7342BA1-3D and EB7342BA1-3F, were able to lase at slightly higher temperatures of 119, 117, and 120 K, respectively. However, the lasing wavelength for device EB7342BA1-3E at 119 K was shorter, at 13.11 μm (similarly for device EB7342BA1-3D). This is due to the band filling effect, as shown in the insets in
Compared with devices with the 7289 wafer, those with the 7342 wafer consistently lased with significantly higher threshold current densities, and only in pulsed-mode operation, though they have the same waveguide structure with identical doping profile. The threshold voltage for devices made from the second ICL wafer was ˜7.5 V at 80 K and increased at higher temperatures due to the rapid increase of threshold current as shown in
InAs-based ICLs having improved device performance at emission wavelengths near 11 μm have been disclosed. Furthermore, a modified QW active region has been implemented into an ICL structure and has enabled ICL operation beyond 13 μm, which confirmed a theoretical prediction and paved the way to further exploration of ICLs in the long-wavelength region. For a wide range of practical applications, these long-wavelength ICLs need to be capable of operating at room temperature.
7541, 7547, 7523, and 7539 Wafers
Four ICL wafers, EB7541, EB7547, EB7523, and EB7539, were grown by MBE on InAs substrates, all of which incorporated the advanced waveguide, and two of which, EB7523 and EB7539, included the InA0.5P0.5 barriers in the QW active region. For EB7541 (EB7547), a regular W-QW structure was used, consisting of a layer sequence of AlAs0.89Sb0.11/InAs/Ga0.65In0.35Sb/InAs/AlAs0.89Sb0.11, with thicknesses of 22/35(36.5)/28/31(31.5)/12 Å. For EB7523 (EB7539), the active region had a layer sequence of AlAs0.89Sb0.11/InA0.5P0.5/InAs/Ga0.65In0.35Sb/InAs/InA0.5P0.5, with thicknesses of 19/16/25(26)/28/20/16 Å in the growth direction. Here the InAs layer thicknesses in the latter wafers EB7523 and EB7539 were reduced by about 30% in the first InAs QW and about 35% in the second InAs QW compared to the devices made from wafers EB7541 and EB7547 which did not include InA0.5P0.5 barriers. Based on a 2-band k·p model, the estimated wavefunction overlaps for EB7541 and EB7547 were 16.7% and 15.6%, respectively. The inclusion of the InA0.5P0.5 barriers in the QW active region in EB7523 and EB7539 increased the estimated overlap to 19% and 18.2%, respectively. The band edge diagrams of one cascade stage for each of the two representative device structures (EB7541 and EB7523) are shown in
There were some uncertainties in the expected operating wavelength for InAs-based ICLs that incorporated the advanced waveguide and those that utilized the modified QW active region, which chiefly manifested in high internal absorption losses, leading to relatively large Jths, low EQEs, low output powers, and limited temperature performance. Therefore, several adjustments to the waveguide were made to reduce the internal loss and to better confine the optical wave within the QW active region. Since the expected emission for these ICLs was to be beyond 11 μm at higher operating temperatures, the waveguide layer thicknesses were slightly increased. Compared to the previous design, the thicknesses of the individual components were increased by about 18%, 5%, and 7% for the InAs SCL, InAs/AlSb SL intermediate cladding, and the ntInAs plasmon cladding layers, respectively. To further reduce losses due to free carrier absorption in the n+-InAs plasmon cladding, the doping concentration there was reduced by about 13%. Also, the doping in the injection region was reduced by about 31%. The calculated optical modal profile and refractive index based on a slab waveguide model for a representative device (EB7541) are shown in
The ICL wafers were grown by molecular beam epitaxy using solid sources except for P, which was supplied by a cracking phosphine injector. All layers were grown at 440° C. Growth rates were approximately 1.0 μm/hr for InAs and InAsP and 0.49 μm/hr for AlAsSb, GalnSb, and GaSb. The intermediate cladding layers were nominally InAs/AlSb superlattices, but since the As source valve was left open during the cladding AlSb layer growth and the As source shutter does not fully block the As flux, layers nominally grown as AlSb contained substantial As, which was accounted for in separate lattice matching calibration growths. The As source valve was closed during critical portions of the active region growth.
The material quality was analyzed using XRD, and the surface morphology was characterized by DIC microscopy. The XRD spectra were measured using a Panalytical X'Pert3 MRD. Symmetric scans along the (004) axis were obtained and show reasonable agreement with the simulated spectra, as shown in
The grown wafers were fabricated into 100-μm-wide (e.g. EB7523BA3-2F, EB7539BA2-2D, EB7541BA3-3H, and EB7547BA3-2A) and 150-μm-wide (e.g., EB7541BA3-1G, EB7547BA3-3C, EB7539BA2-2A) BA mesas using standard UV contact photolithography and wet chemical etching. The wafers were left unthinned and cleaved into approximately 1.5 mm-long laser bars without facet coating, which were mounted epi-side up on copper heat sinks for testing.
The fabricated devices were tested using a Nicolet FTIR, with CW power measurements carried out with a PM3 Coherent PowerMax thermopile power meter, in which the beam divergence loss was not included. Hence, the reported output power and EQE of the devices are conservative. Multiple devices from each of the four ICL wafers operated in both CW and pulsed modes, as shown in
Wafers EB7541 and EB7547 both included the advanced waveguide, but did not include InA0.5P0.5 barriers in the QW active region. In CW mode, two devices from EB7541 had threshold current densities as low as 12 A/cm2 at 80 K, representing about a 50% reduction compared to previous ICLs operating at similar wavelengths. These ICLs lased at 10.2 μm at 80 K and then red shifted to longer wavelengths at high temperatures. The characteristics of a representative device, EB7541BA3-3H, are shown in
Compared to ICLs from EB7541, devices from wafer EB7547 lased at longer wavelengths as expected due to the slightly wider InAs QWs, and they had higher Jth and somewhat degraded temperature performance as shown in
Considering both wafers had the same waveguide, doping concentrations, and nearly identical active region designs, the small difference in the InAs QW width only resulted in an approximately 6.9% shift of lasing wavelength at 80 K. Hence, similar band structure, differential gain, and transparency current density would be expected for both. Consequently, they should have comparable threshold current density. This is also due to the fact that the free-carrier absorption loss difference between them is less than 20% based on the simulation shown in Table 1, which is supported by the comparable EQEs observed for them at 80 K, as shown in
Wafers EB7523 and EB7539 both included the advanced waveguide as well as the InA0.5P0.5 barriers in the QW active region. Multiple devices from both wafers lased in both CW and pulsed modes. A representative device EB7523BA3-2F lased in CW mode up to 90 K, with an emission wavelength of 12.2 μm and a Jth of about 138 A/cm2 as shown in
In pulsed mode, this device lased at 80 K at 11.8 μm, with a Jth of about 44 A/cm2, which was reduced by a factor of nearly 4 compared to the previous ICL, while its EQE reached 451% at 80 K (
A representative 100 μm-wide device from wafer EB7539 also operated in CW mode up to 85 K with a Jth of about 143 A/cm2 and at a lasing wavelength of 12.4 μm (
In pulsed operation, a 150 μm-wide device (EB7539BA2-2A) lased at 80 K with a Jth of about 64 A/cm2, which is reduced about three times compared to the previous ICL from wafer 7342 with InAsP layers, and 45% higher than that of EB7523BA3-2F. Furthermore, this device lased in pulsed mode up to 150 K at 13.1 μm with a Jth of about 1111 A/cm2. The extracted EQE in pulsed mode was about 341% at 80 K before dropping to about 9% at 150 K as shown in
Compared to wafers 7289 and 7342, modifications in the latter 4 wafers to the waveguide, including layer thickness changes and doping concentration adjustments, resulted in enhanced device performance in the 10-13 μm wavelength region. Furthermore, the ICLs that included the active layer design change exhibited CW operation beyond 12 μm, which is the first demonstration of BA ICLs operating in CW mode at such long wavelengths. Several ICLs with this P-containing barrier have been explored with varying InAs and InA0.5P0.5 layer thicknesses, which have helped to pave the way for better understanding of the expected lasing wavelength for this new kind of ICL. For practical applications, these long-wavelength ICLs need to be capable of operating near room temperature, or at least at temperatures accessible by thermoelectric cooling. With additional adjustments such ICLs should be able to achieve better performance in the 10-13 μm range at elevated temperatures.
While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, components, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled may be directly coupled or may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.
This claims priority to U.S. Prov. Patent App. No. 63/312,238 filed on Feb. 21, 2022, which is incorporated by reference.
This invention was made with government support under Contract Number 1931193 awarded by the National Science Foundation (NSF) and under Contract Number DE-NA0003525 awarded by the U.S. Department of Energy/National Nuclear Security Administration. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63312238 | Feb 2022 | US |
