Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathin films

Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathinfilmsL. J. Brillson

Citation: Journal of Vacuum Science & Technology B 19, 1762 (2001); doi: 10.1116/1.1394728 View online: http://dx.doi.org/10.1116/1.1394728 View Table of Contents: http://scitation.aip.org/content/avs/journal/jvstb/19/5?ver=pdfcov Published by the AVS: Science & Technology of Materials, Interfaces, and Processing Articles you may be interested in Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cellson ZnO:Al J. Appl. Phys. 113, 044519 (2013); 10.1063/1.4789599 Impact of solid-phase crystallization of amorphous silicon on the chemical structure of the buried Si/ZnO thin filmsolar cell interface Appl. Phys. Lett. 97, 072105 (2010); 10.1063/1.3462316 Characterizing nanometer-sized V -defects in InGaN single quantum well films by high-spatial-resolutioncathodoluminescence spectroscopy Appl. Phys. Lett. 94, 131908 (2009); 10.1063/1.3104850 Thin-film wafer fusion for buried-heterostructure InP-based lasers fabricated on a GaAs substrate J. Appl. Phys. 87, 2857 (2000); 10.1063/1.372269 Spatially resolved luminescence studies of defects and stress in aluminum gallium nitride films Appl. Phys. Lett. 71, 3841 (1997); 10.1063/1.120520

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Nanoscale luminescence spectroscopy of defects at buried interfacesand ultrathin films

L. J. Brillsona)

Department of Electrical Engineering, Department of Physics, and Center for Materials Research,205 Dreese Lab, 2015 Neil Ave., The Ohio State University, Columbus, Ohio 43210

~Received 13 April 2001; accepted 25 June 2001!

Low energy electron-excited nano-luminescence~LEEN! spectroscopy provides electronic bandgap, confined state, and deep level trap information from semiconductor surfaces and interfaces ona nanometer scale. Correlation of luminescence features with their spatial location inside a growthstructure—either depth wise or laterally—also provides information on the physical origin andgrowth dependence of the electronically active defects that form. LEEN spectroscopy of localizedstates illustrates this approach for a representative set of III–V nitride interfaces, includingmetal-GaN Schottky barriers, GaN/InGaN quantum wells, GaN ultrathin films, AlGaN/GaNpseudomorphic heterostructures across a single growth wafer, and GaN/Al2O3 interfaces. In eachcase, electronic properties are sensitive to the chemical composition, bonding, and atomic structuresnear interfaces and in turn to the specifics of the growth process. ©2001 American VacuumSociety. @DOI: 10.1116/1.1394728#

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I. INTRODUCTION

Semiconductor interfaces and thin films are integral tgrowing array of active electronic structures as dimensishrink into the nanometer regime. Localized electronic stanear such interfaces and films alter electronic properthrough much of a nanoscale structure.1,2 Nevertheless, relatively little is known about these states from direct obsertion. Low energy electron-excited nano-luminescen~LEEN! spectroscopy provides a means of probing loelectronic states within material structures with nanomescale depth dimensions3,4 and yields information availableonly indirectly at best by other electronic techniques. Ehanced with laterally confined electron beams, this technican provide surface and interface electronic properties oeas and volumes with nanoscale dimensions, e.g., clusdots, grains, and morphological features. Furthermore,correlation of luminescence features with their spatial lotion within a growth structure—either depth wiselaterally—can provide information on the physical origin agrowth dependence of the electronically active defectsare present.

Localized electronic states and new dielectric phasesevident at a wide range of semiconductor interfaces aresult of modified atomic bonding, extended chemical retions, and interdiffusion.1,2 Besides the interface statewidely studied at many metal-semiconductor junctions,calized states are present, for example, at interfaces of qtum wells, two-dimensional electron gas~2DEG! structures,and semiconductor-insulator growth templates. Over thefew years, LEEN spectroscopy studies have addressedstates at a wide variety of semiconductor and insulananoscale structures. Here we focus on the III–V nitrsemiconductors to illustrate the nature of localized statesa representative set of interface structures.

a!Electronic mail: [email protected]

1762 J. Vac. Sci. Technol. B 19 „5…, SepÕOct 2001 1071-1023 Õ200

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The III–V nitride compounds are of high current interefor advanced optoelectronic and microelectronic applitions, where piezoelectric as well as confinement properof the nitrides can enhance electronic device performanUsing LEEN in combination with other surface scienmethods, we have probed the localized electronic statemetal-GaN Schottky barriers, GaN/InGaN quantum weGaN ultrathin films, and AlGaN/GaN pseudomorphic hetestructures across a single growth wafer. Their propertiessensitive to the chemical composition, bonding, and atostructures near interfaces and in turn to the specifics ofepitaxial growth process. Cross sectional ultrahigh vacu~UHV! scanning electron microscopy extends this techniqand enables us to determine the nature of degenerate doat nanoscale interfaces of bulk GaN on Al2O3 . In general,the electrically active defects found in multilayer nanostrutures appear to depend sensitively on growth and procesconditions, suggesting new approaches to optimize the inface growth process.

II. LOW ENERGY ELECTRON-EXCITED NANO-LUMINESCENCE SPECTROSCOPY

The LEEN spectroscopy technique involves an incidelectron beam of energyEB that produces free electron-hopair recombination across the band gap or between deepels and the band edges. The depth of excitation increasea scale of tens of nanometers with increasingEB on a keVscale, as determined by energy-range relationships for enloss within a solid.5–7 A useful approximation to theEverhart–Hoff expression for the maximum Bohr–Betrange of energy dissipation isRB5Cja, where j51.1658E/I and E5incident electron beam energy in keV.5 The‘‘mean excitation energy’’ generated by the incident beamdefined asI 5(9.76158.8Z21.19)Z in eV, whereZ is theaverage atomic number of the solid. The material-dependconstant C59.40310212 I 2(A/Z)c8/r, where A5atomic

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weight andr5density.5 For j values below 10,c851.48 anda51.29 provide a fit to experimental data.7 The electron cas-cade produces secondaries whose energies decrease wcreasing penetration depth. The rate of energy loss reachmaximum at intermediate depthsU0 that increase with inci-dent beam energy. The Fig. 1 inset shows several curveenergy loss per unit length,dE/dx, as a function of depthinto a target. These curves represent a polynomial fit toEverhart–Hoff depth-dose relation,5 valid down to a fewhundred eV, andU0 is approximated in Fig. 1 as 0.31RB .Other models6,7 exhibit similar proportionalities ofU0 withRB . The polynomial fit to the Everhart–Hoff function yieldRB andU0 values in good agreement with Monte Carlo cculations and provides a basis for extending the fit to lenergies.8

Figure 1 shows the energy dependence ofRB andU0 forGaN in the low keV range. For this material,I5219.05 eV, r56.15 g/cm3, Zaverage519, and Aaverage

541.86 gm/mole, so thatC52.39 in nm. The Bohr–Bethemaximum rangeRB;50 nm forEB52 keV and;20 nm at 1keV. Correspondingly,U0;17 nm for 2 keV and;7 nm for1 keV. Thus excitation depth varies on a nanometer scalthe 1 keV range. The inset illustrates the overall shape ofrate of energy loss and electron-hole pair creation generby the electron cascade. Furthermore, since free carrierfusion length prior to recombination determines overall re

FIG. 1. Calculated Bohr–Bethe maximum range of excitationRB and depthof maximum energy lossU0 for incident electrons of energyEB in GaN.Expressions forRB andU0 are based on the energy loss rate per unit plength derived by Everhart and Hoff~see Ref. 5!.

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lution and the diffusion length of minority carriers in Gananostructures is quite short~e.g., ,30 nm!,9 LEEN spec-troscopy can provide depth profiles of near band edge~NBE!and defect emission intensity with depth resolution less tseveral tens of nanometers.

Figure 2 illustrates the key features of the LEEN tecnique. At lower left is a schematic cross section of the spemen in a UHV chamber, a glancing incidence electron gwith EB in the range 0.1–4 keV, near infrared to ultraviol~UV! optics, a Leiss prism monochromator, and one of seral photodetectors. Scanning electron microscopy~SEM!studies employed a JEOL JAMP-7800 UHV scanning eltron microscope withEB of 0.5–25 keV at constant excitation power of 1mW, an Oxford MonoCL grating monochromator, and near-UV photomultiplier tube. Depending onEB

and the specimen structure, the incident beam exciteselectron-hole pairs above, at, or below an interface~upperleft!. At upper right, the subsequent radiative recombinattakes place between conduction and valence bands (hv3),from new phases, compounds, or ultrathin layers with diffent dielectric properties (hv2), or between band edges anstates within the band gap (hv1). Thus, the optical featureof the emitted light and its depth dependence can provinformation on the physical nature of the localized interfastates.

III. METAL-SEMICONDUCTOR INTERFACES

Relatively few studies of Schottky barrier formation habeen carried out for metals on GaN compared with GaAsother III–V compound semiconductors. Conventional eletrical measurements and surface science studies have sthat Fermi level (EF) movement can occur over a widerange than with, e.g., GaAs, although the range is less tfor ideal ‘‘Schottky-like’’ behavior.9–11 This behavior is dueto localized states that restrictEF movement and introducedipoles at the interface. Yet little is known of the electron

FIG. 2. Schematic illustration of the LEEN spectroscopy technique. An etron beam incident on the specimen induces light emission correspondinoptical transitions involving localized states, near band edge states, anddielectric phases. With increasing energy on a sub-keV scale, the elebeam penetrates deeper into the solid on a nanometer scale, probing aat, or below a buried interface or thin film.


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structure or chemical bonding at the intimate interfaLEEN spectra provide a measure of these localized stbelow the free surface that indicates more than one physbasis for theEF behavior.

Figure 3 illustrates LEEN spectra for a clean, low eneelectron diffraction~LEED!-ordered GaN~0001! ~131! sur-face overcoated with 30 ML of Al in UHV and annealed1000 °C.12 For this overlayer, the interface is located;9 nmbelow the free surface. The three spectra shown illustemission withEB andU0 corresponding to excitation abovenear, and below the Al–GaN interface. The main peak fture at 3.42 eV corresponds to the near band edge transcharacteristic of bulk GaN. AtEB corresponding to excitation primarily near the Al–GaN interface, a new peak featuappears at an energyabovethe band gap. The inset displaya magnified version of this feature. Since this feature canbe accounted for by states in the GaN band gap, the speindicate the formation of a new dielectric phase. The 3.85feature may be due to near band edge transitions fromAlGaN alloy or deep level transitions from AlN. Near banedge transitions from AlN at 6.2 eV are not observed, sgesting instead that an alloy forms. Indeed, such peak egies are observed in AlxGa12xN alloy films grown intention-ally and correspond to compositions ofx50.15– 0.2.13 Ineither case, the depth dependence shown in Fig. 3 indicthat a chemical reaction occurs at the intimate Al–GaNterface, resulting in a new dielectric phase that would c

FIG. 3. LEEN spectra of 30 ML of Al on LEED-ordered GaN~131! surfaceannealed to 1000 °C in UHV. The above-band-gap peak at 3.85 eV indicthe formation of an AlGaN alloy. The energy dependence confirms its lotion at the buried interface depth~30 ML Al ;9 nm!. After Younget al. ~seeRef. 12!.

J. Vac. Sci. Technol. B, Vol. 19, No. 5, Sep ÕOct 2001


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tainly alter the Schottky barrier expected from an abrupt AGaN interface alone.

Extrinsic states of a different nature are evident for MgGaN interfaces. 30 ML of Mg deposited on a clean, LEEordered GaN~0001! ~131! surface and annealed at 1000 °induces new emission only at energies below the GaN nband edge transition~not shown!.12 Again, such emissionreaches a maximum forEB and U0 corresponding to theburied interface region. Broad emissions appear at enerof 1.4, 1.6, and 2.15–2.2 eV, corresponding to deep levelthe midgap range. The 2.15–2.2 eV emission is in goagreement with soft x-ray photoemission spectroscopy obvations that showEF stabilization at 2.2 eV above the valence band maximum. The LEEN spectroscopy resultsMg and Al on GaN are evidence that extrinsic electronstates—whether by atomic rebonding or lattice defformation—are an important factor at GaN Schottky barrie

IV. QUANTUM WELL INTERFACES

Localized states form not only at metal-semiconducjunctions, but also at semiconductor heterojunctions. As wSchottky barriers, the presence of such states and assocdipoles can alter band bending and band lineups betweeninterface constituents. For optoelectronic structures suchquantum wells, such states can have an additional, negaimpact by introducing new recombination pathways thcompete with emission in nearby carrier-confined structuThe LEEN technique provides a tool to gauge the electroquality of ultrathin materials: the degree of charge trappdue to defects, the diffusion length of free carriers, andproportion of piezoelectrically strained versus unstrainedgions within individual layers of a multilayer structureAgain, by using electron beam energies well below thosecathodoluminescence, one can distinguish between esions from different layers each only tens of nanometthick. While such layers are integral to next-generation ligemitters and high-speed transistors, their performance issensitive to the parameters of epitaxial growth. LEEN sptroscopy can guide improvements in such growth and subquent processing by identifying specific defective layers ainterfaces in the multilayer stack.

Figure 4 illustrates the contrast in emission versus defor a single 2 nm InGaN quantum well located 30 nm beloa free GaN surface.13,14 Ratios of LEEN intensities for aGaN/InGaN/GaN quantum well gauging the quantum wemission at 2.6 and 2.8 eV versus GaN near band edge esion at 3.4 eV and their intensities relative to the well-know‘‘yellow’’ defect emission at 2.2 eV exhibit pronouncechanges with depth that are characteristic of layer-specelectronic quality~e.g., densities of impurities, point and etended lattice defects!. Figure 4 illustrates how quantum weemission increases as excitation depth approaches that oquantum well, while the GaN emission decreases cospondingly. These variations withEB and depth also show~1! clear differences in trap concentration between an ulthin epilayer and the underlying substrate,~2! a characteristiconset in quantum well emission with depth that determin

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the minority carrier diffusion length~525–28 nm!. HigherIn alloy quantum wells with higher lattice mismatch to Gareveal emission from a nm-thick layer of a second crystagraphic phase~i.e., cubic versus wurtzite! localized belowthe free surface at the lattice-mismatched interface.13 Suchelectronic, chemical, and structural information woulddifficult to obtain nondestructively if at all via other techniques, e.g., fabrication of an electronic transport devstructure or cross sectional electron microscopy. Perhmost significant is the clear distinction between differenanometer-scale layers obtained via changes inEB . Theseclear differences with depth make it possible to understhow chemical bond defects produce deep levels that promelectronic recombination and trapping. In turn, this chemibasis can guide the epitaxial growth of light-emitting marials such as GaN/InGaN/GaN quantum wells to contthese recombination centers during the layer-by-layer epiial growth process of opto-or microelectronic structures.

V. TWO-DIMENSIONAL LAYER STRUCTURES

The depth-resolved LEEN technique has proven usefudetermine the defects within each of the heterojunction lers of a two-dimensional electron gas~2DEG! confinementstructure. By exciting optical transitions at controlled dep

FIG. 4. LEEN spectra of a 2 nm GaN/In0.14Ga0.86N/GaN single quantum welllocated 30 nm below the free GaN surface. With increasingEB , the quan-tum well emission increases then decreases relative to the GaN NBE esion, indicating the nanoscale nature of the LEEN excitation. After Brillset al. ~see Refs. 13 and 14!.



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from a free surface of AlGaN grown epitaxially on Ga~0001!, one can obtain a direct measure of deep level engies and densities within each of the multiple layers. Omeasurements demonstrate that defects localized within25-nm-thick confinement layer have a dramatic effect on2DEG carrier concentration within the nearby space charegion of the AlGaN/GaN interface. We used incident eletron beam energies of 0.5–15 keV from our UHV scannielectron microscope~SEM! to compare structures grown under nearly identical conditions yet with drastically differeelectronic properties. AlGaN heterostructures of 25 nthickness and nominal 30% Al concentration were grownGaN buffer layers on sapphire substrates by plasma-assmolecular beam epitaxy and capped with a 2 nm GaNlayer.Polarization-induced electron densities at the AlGaN/Ginterface ranged from;131013cm22 to zero and room tem-perature mobilities ranged from 570 to 1480 cm2/V s, despitenearly identical growth conditions.

LEEN spectra provide evidence for defects in these strtures that can account for the different electrical propertFigure 5 shows a clear contrast in defect emissionsAlGaN/GaN 2DEG structures with versus without carriconfinement.15,16 The 2.34 eV emission evident in Fig. 5~a!reaches its maximum intensity for depths correspondingthe 25 nm AlGaN film. It is absent in Fig. 5~b!, where the2DEG layer is present. These defects within the AlGaN ficompletely alter the electronic band bending so that thcharges are no longer confined. The differences betweencessful and failed structure LEEN depth profiles highligthe importance of charged defects near quantum-confinedgions. LEEN also reveals high strain in the 2-nm-thick Gacap layer with evidence for a Franz–Keldysh redshift~3.27eV surface versus 3.42 eV bulk! due to piezoelectric charging. The ultrathin GaN cap layer also exhibits the presenca deep level near midgap, as evidenced by the strong esion seen in both Figs. 5~a! and 5~b! at the lowestEB . Thesemeasurements illustrate the unique ability of LEEN spectrcopy to probe electronic defect states in ultrathin layers.

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FIG. 5. Depth-dependent near band edge and defect emissions fromAlGaN/GaN 2DEG structures. The deep level emission at AlGaN ladepths in~a! vs ~b! corresponds to the absence of 2DEG carrier confinemFranz–Keldysch shifts of GaN emission due to piezoelectric strain aredent at 3.25–3.43 eV near the free surface in both cases~see Refs. 15 and16!.


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The deep level features in Fig. 5 are sensitive to epitagrowth conditions and can even vary with position acrossingle wafer. LEEN spectra with the spatial resolution oSEM permits one to determine such lateral effects andprinciple, their root causes. In Fig. 6, 2 keV spectra tmaximize emission from the AlGaN layer exhibit substantvariations in defect intensity versus wafer radiusRw across arelatively high quality 22.5 mm wafer~maximum spz

51.7731013e/cm2 and m5447 cm2/V s, specimen C!. Thedeconvolved deep level spectra exhibit 2.34 and 2.18peak intensities that vary independently.~The 1.9 eV ‘‘peak’’is a second order feature.! Al xGa12xN near band edge~NBE!intensities grow withRw and AlxGa12xN peak energies shiffrom 3.7 to 3.95 eV with increasingRw , indicating higher Allayer content in the AlxGa12xN nearer the wafer edge. Sucvariations in deep level intensities can be used to determoptimal radii with which to prepare device structures.

The changes in defect emission correlate with chemcomposition of these AlGaN/GaN heterojunctions onnanoscale. Auger electron spectroscopy~AES! with depthprofiling at glancing angles and low energies yield profilesthe AlGaN films and their interfaces with the underlyinGaN. AES reveals startling differences in the interfaabruptness shown in Fig. 7, ranging from less than 1 tonm.17 In turn, the interdiffused junctions exhibit LEEN emission at the AlGaN band gap characteristic of lowerconcentration—i.e., lower NBE energy and a variation in

FIG. 6. LEEN spectra vs radius for a wafer with 2DEG. Dashed lines incate deconvolved defect peaks. After Bradleyet al. ~see Refs. 16 and 17!.



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NBE energy with depth–versus the chemically abrupt jutions. Perhaps most significantly, the interdiffused junctioalso correlate with the appearance of defects within theGaN and the disappearance of the 2DEG. Electrostatic meling of the conduction band structure within each layshows that the AlGaN defects produce charge densities cparable to the 2DEG densities. Thus, atomic interdiffuson a nanoscale generates optically active defects that inence band bending and carrier confinement. More broadepth-resolved LEEN spectra provide a tool to assess groof semiconductor structures whose properties depend ccally on sharp chemical interfaces.

VI. SEMICONDUCTOR-INSULATOR GROWTHTEMPLATES

It is now possible to obtain profiles of electronic defectssemiconductor-insulator interfaces that are linked to atodiffusion across their junction. The nature of atomic bondiand local electronic structure at GaN heterojunction intfaces has assumed increased significance as crystal quimproves and advanced wide-gap semiconductor devscale down to the nanometer regime. GaN interface reactand defect formation are of critical importance in controllincarrier transport through the epitaxial thin films, particulanear the growth substrate. Cross sectional secondary eleimaging, cathodoluminescence spectroscopy~CLS!, andCLS imaging of GaN grown by hydride vapor phase epita~HVPE! on sapphire reveal defects that are present witeither the GaN or the sapphire and that reach their maximdensity at the GaN/sapphire interface.18,19 We have probedthe electronic defects and compositional band gap channear GaN/Al2O3 interfaces on a nanometer scale using lotemperature~10 K! CLS. Defect emissions appear to vasystematically with known electronic properties of a wirange of GaN grown on HVPE sapphire. In particular, shcarrier densities extending over two orders of magnitudethe ‘‘buried’’ interface of a wide range of junctions correlatewith the defect and chemical bonding features obserspectroscopically.18 Electrochemical capacitance–voltag(ECV) profiling of Look20 provided epitaxial sheet carriedensities localized near GaN/Al2O3 interfaces. In addition,our temperature-dependent CLS spectra exhibited dobound exciton transitions at 26 meV~3.447 eV in Fig. 8!characteristic of O impurities that are spatially localizedthe interface.19 Furthermore, its intensity profile matches thof the increased carrier concentration measured by ECVthe O profile measured by secondary ion mass spectrom~SIMS!—thereby providing a consistent picture of the doing by O diffusion from Al2O3 into GaN over 100–200 nmWe also found evidence for a nanoscale chemical reactioAl with GaN at its Al2O3 interface that may promote formation of these shallow donors along with Al–GaN alloyinFor interfaces with highest doping concentrations, CL sptra show above band gap emission due tobothband filling aswell as AlGaN alloy formation—similar to features showe.g., in Fig. 3 here. Indeed, the alloying, band gap variatioand defect formation revealed by these techniques sug

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that the chemical rebonding and doping phenomena masignificant for semiconductor-insulator interfaces in gene

Besides these examples of localized states at GaN infaces, LEEN and CL spectroscopies have highlighted a nber of other surface and interface phenomena involving GThese include: impurity-activated light emission at Er-dopGaN,21,22 control of defects at GaN surfaces,23,24 develop-ment of an In capping technique for preserving clean,dered GaN during air exposure,25 and measurement of neaband edge and defect spectra at molecular beam epgrowth temperatures.26

Beyond the III–V nitrides, LEEN spectroscopy studihave extended to defect states at ultrathin SiO2 oxides27 andoxynitrides,28 the effect of radiation damage on gaoxides,29 the diffusion of impurities below the SiC surface,30

the removal of near-surface defects in TiO2 and ZnO withsurface chemical processing,31 and the oxidation of ultrathinfilms inside tunneling magnetoresistive structures.32 Scan-ning electron microscope techniques at low and variableergies are now extending this technique to quantum clusdots, morphological features, as well as the electronic effthat arise at their various structural and chemical

FIG. 7. AES depth profiles of an AlxGa12xN/GaN interface vs growth waferadius for ~a! Rw521 mm ~near the wafer edge,~b! Rw518 mm, and~c!Rw515 mm. After Bradleyet al. ~see Ref. 17!. Increasing temperature alower radii ~bottom panel! leads to Al–Ga interdiffusion~2 min correspondsto 10 nm! and defect formation.



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terfaces. The combination of SIMS with SEM-based LEEand CLS will enable process-dependent studies of checally induced electronic effects at semiconductor doping lels, i.e., less than parts per million, such as diffusion-induimpurity, point defect, and defect complex formation. Wior without laterally confined beams, LEEN can serve as ainsitu diagnostic tool to monitor electronic material qualiduring chemical processing, to qualify growth structurprior to device fabrication, and to identify defects and failumechanisms due to thermal or chemical stress. Hence, tnanoscale luminescence techniques are versatile enougaddress a wide array of solid state phenomena.

VII. CONCLUSIONS

Electron-excited nanoscale luminescence spectroscohave the ability to measure properties of localized electrostates near surfaces and interfaces. These spatially locameasurements permit researchers to determine which laor interfaces give rise to the charge sites that can dominband bending, free carrier recombination, carrier confiment, and charge transport. Depth-dependent correlationstween emission features and their spatial location can eldate the physical origins of such states. In turn, t

FIG. 8. Low temperature CL spectra of a HVPE-grown GaN film on Al2O3

showing interface-specific donor-bound exciton peak at 34 meV andcrease of donor-like features within 1mm of the sapphire interface. AfteGosset al. ~see Ref. 19!.


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information can provide new strategies to guide the epitagrowth of advanced electronic material nanostructures.

ACKNOWLEDGMENTS

The authors gratefully acknowledge support in part byOffice of Naval Research, the Air Force Office of ScientiResearch, the Department of Energy~depth-dependent measurements!, and the National Science Foundation.

Presented at the 28th PCSI Conference, Lake Buena Vista, FL, 7–11ary 2001.

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Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathin films

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Transcript of Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathin films