DTIC ADA579956: Light-Hole and Heavy-Hole Transitions for High-Temperature Long-Wavelength Infrared Detection

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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Light-hole and heavy-hole transitions for high-temperature W911NF-08-1-0448
long-wavelength infrared detection
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
611102
6. AUTHORS 5d. PROJECT NUMBER
Y. F. Lao, P. K. D. D. P. Pitigala, A. G. U. Perera, H. C. Liu, M.
Buchanan, Z. R. Wasilewski, K. K. Choi, P. Wijewarnasuriya 5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAMES AND ADDRESSES 8. PERFORMING ORGANIZATION REPORT
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Georgia State University
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Georgia State University Research Foundation, Inc.
Atlanta, GA 30302 -3999
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14. ABSTRACT
Hole transitions from the heavy-hole (hh) to the light-hole (lh) band contributing to the 4–10??m response range
are reported on p-GaAs/AlGaAs detectors. The detectors show a spectral response up to 16.5??m, operating up to a
temperature of 330 K where the lh-hh response is superimposed on the free-carrier response. Two characteristic
peaks observed between 5–7??m are in good agreement with corresponding energy separations of the lh and hh
bands and thus originated from lh-hh transitions. Results will be useful for designing multi-spectral detection which
15. SUBJECT TERMS
aluminium compounds, energy gap, gallium arsenide, III-V semiconductors, infrared detectors
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 15. NUMBER 19a. NAME OF RESPONSIBLE PERSON
a. REPORT b. ABSTRACT c. THIS PAGE ABSTRACT OF PAGES Unil Perera
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404-413-6037
Standard Form 298 (Rev 8/98)
Prescribed by ANSI Std. Z39.18
Report Title
Light-hole and heavy-hole transitions for high-temperature long-wavelength infrared detection
ABSTRACT
Hole transitions from the heavy-hole (hh) to the light-hole (lh) band contributing to the 4–10??m response range are
reported on p-GaAs/AlGaAs detectors. The detectors show a spectral response up to 16.5??m, operating up to a
temperature of 330 K where the lh-hh response is superimposed on the free-carrier response. Two characteristic
peaks observed between 5–7??m are in good agreement with corresponding energy separations of the lh and hh bands
and thus originated from lh-hh transitions. Results will be useful for designing multi-spectral detection which could
be realized on a single p-GaAs structure.
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Light-hole and heavy-hole transitions for high-te ...
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© 2010 . Published in Applied Physics Letters, Vol. Ed. 0 97, (9) (2010), (, (9). DoD Components reserve a royalty-free,
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APPLIEDPHYSICSLETTERS97,091104(cid:2)2010(cid:3)
Light-hole and heavy-hole transitions for high-temperature long-wavelength
infrared detection
Y. F. Lao,1 P. K. D. D. P. Pitigala,1 A. G. U. Perera,1,a(cid:2) H. C. Liu,2 M. Buchanan,2
Z. R. Wasilewski,2 K. K. Choi,3 and P. Wijewarnasuriya3
1DepartmentofPhysicsandAstronomy,GeorgiaStateUniversity,Atlanta,Georgia30303,USA
2InstituteforMicrostructuralSciences,NationalResearchCouncil,Ottawa,OntarioK1A0R6,Canada
3U.S.ArmyResearchLaboratory,Adelphi,Maryland20783-1197,USA
(cid:2)Received 15 June 2010; accepted 16August 2010; published online 2 September 2010(cid:3)
Holetransitionsfromtheheavy-hole(cid:2)hh(cid:3) tothelight-hole(cid:2)lh(cid:3) bandcontributingtothe4–10 (cid:2)m
response range are reported on p-GaAs/AlGaAs detectors.The detectors show a spectral response
up to 16.5 (cid:2)m, operating up to a temperature of 330 K where the lh-hh response is superimposed
on the free-carrier response. Two characteristic peaks observed between 5–7 (cid:2)m are in good
agreement with corresponding energy separations of the lh and hh bands and thus originated from
lh-hh transitions. Results will be useful for designing multi-spectral detection which could be
realized on a single p-GaAs structure. © 2010 American Institute of Physics.
(cid:4)doi:10.1063/1.3486169(cid:5)
Recently, uncooled 3–5 (cid:2)m detectors based on hole between the barrier bottom and the Fermi level (cid:2)or the
transitions from the light/heavy hole (cid:2)lh/hh(cid:3) bands to the valence-bandedgeiftheFermilevelisaboveit(cid:3)ofemitters,
spin-orbit split-off (cid:2)so(cid:3) band were reported1,2 using and determines the threshold wavelength (cid:2)(cid:4)(cid:3). The spectral
t
p-GaAs/AlGaAs structures.This mechanism can provide an limitation comes from the requirement of photon-energy
extended spectral range by varying the materials with differ- greater than (cid:3) , e.g., 0.341 eV for GaAs. On the contrary,
so
entso splittingenergies(cid:2)(cid:3) (cid:3).Forexample,III-Vphosphide lh-hh transition energy has a high onset due to their maxi-
so
material will allow 8–14 (cid:2)m detection (cid:2)e.g., (cid:3) (cid:2)GaP(cid:3) mum separation (cid:3) (cid:2)(cid:5)(cid:3) (cid:2)Refs. 10 and 11(cid:3) in the (cid:6)111(cid:7)(cid:2)(cid:5)(cid:3)
so 1
=0.08 eV(cid:3). As a result of spin-orbit interaction, the lh and direction,butnominimumlimitationfromtheband-structure
hh bands are also separated with an energy approximately point of view. Therefore, lh-hh transitions can theoretically
approaching (cid:2)2/3(cid:3)(cid:3) at wave vectors (cid:2)k(cid:3) away from the produce broad absorption features up to the wavelength re-
so
Brillouin Zone (cid:2)BZ(cid:3) center. Hole transitions between gion where FCAbecomes dominating.
these two bands can lead to optical absorption at wave- Thedetailedvalence-bandstructureofGaAsisshownin
lengths up to 10 (cid:2)m for p-GaAs.3 In this letter, attention is Fig.1(cid:2)a(cid:3)toillustratevariousIVBAprocesses.Threetypesof
paid to spectral response due to lh-hh transitions in hole transitions, i.e., from hh→so, lh→so and hh→lh, can
p-GaAs/AlGaAs detectors, showing attractive applications
for mid- and long-wavelength infrared (cid:2)MWIR and LWIR(cid:3)
Energy(eV)
detection.
0.60.30.2 0.1
Research on MWIR and LWIR detectors such as
imnferracruerdy-pchadomtoiduemtectteolrlusri(cid:2)dQeW(cid:2)MIPC5Tan(cid:3),d4 qQuDanIPtu6m(cid:3),-twypelel-IaInIdnAdost/ (a)←lhhh←lhhh←sohh←solh ←lhhh Ef h(bh)→sohh→lh 1 104−1m)
GaSbstrainedlayersuperlattice(cid:2)SLS(cid:3)7andquantumcascade 2 c
hh (
detectors(cid:2)QCD(cid:3)8isstillinprogress,whereinuniformity,low band 3 nt
e
cacopansptdl,iicdaaanttideo.nmsT.uhlAetissdpaeetcemtcrataotlursdreedtmeecmatitooenrnisatarlaresteyddsteehsmierra,ebGlheaaAvfoseriasprssaiucmctihiclaaarl Energy (3) Δ′0 (2) 103ffiCoeci
structure to the standard9 heterojunction interfacial work- (1) Δ1 4 102 on
function internal photoemission detector which consists of lh→so pti
alternative highly p-doped absorbing layers (cid:2)emitters(cid:3) and lh or
undoped barriers. The highly doped and thick emitters (cid:2)18.8 band bs
nm(cid:3) will lead to three-dimensional energy states as opposed basond 101 A
toquantizedstates.Carriersexcitedbyincomingradiationin Λ Γ Δ 4 8 12 16
a split-off detector1,2 originate from hole transitions taking Wavevector Wavelength(μm)
place either between different bands (cid:2)intervalence-band ab-
sorption, IVBA(cid:3), specifically from the hh band to the so FIG.1. (cid:2)Coloronline(cid:3)(cid:2)a(cid:3)Schematicofthevalence-bandstructurealongthe
band, or within the same band (cid:2)free-carrier absorption, directionof(cid:6)111(cid:7)(cid:2)(cid:5)(cid:3)and(cid:6)100(cid:7)(cid:2)(cid:3)(cid:3).VariousIVBAtransitionsareindicated.
The (cid:2)1(cid:3), (cid:2)2(cid:3), and (cid:2)3(cid:3) represent lh-hh transitions at different wave vectors.
FCA(cid:3).Thesecarriersthenescapeoverthebarriersbyapho- TheFermileveliscalculatedfor3(cid:6)1018 cm−3p-dopedGaAsat80K.(cid:2)b(cid:3)
toemission process occurring at the emitter-barrier interface. Measured room-temperature absorption spectra of p-GaAs compared with
The internal work function is defined by energy difference thecalculatedFCAcurvesplottedbydashedlines.Alsoshownisdatafrom
Refs. 3 (cid:2)curves 1(cid:3) and 13 (cid:2)curve 4(cid:3); the doping levels for curves 1–4 are
2.7(cid:6)1019 cm−3, 8.0(cid:6)1018 cm−3, 3.0(cid:6)1018 cm−3, and 2.7(cid:6)1017 cm−3,
a(cid:3)Electronicmail:[email protected]. respectively.
0003-6951/2010/97(cid:3)9(cid:2)/091104/3/$30.00 97,091104-1 ©2010AmericanInstituteofPhysics
Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
091104-2 Laoetal. Appl.Phys.Lett.97,091104(cid:3)2010(cid:2)
1.6 lh-hh(2) /AW)0.18 Bias:0.2V (a) (b) 1.5
so-hh lh-hh(1) m
( SP2,80K
/AW) 1.2 6V ponsivity0.09 a.u.) λt=6.5μm 3S3P03K 1.0/AW)
vity(m 0.8 Res 03Wavele6ngth(μm9) sivity( λStP=19,.830μKm 2S4P02K vity(m
iRespons 0.4 42VV SP1 Respon λ1t3=3125,.500μKm 1S7P01K 0.5Responsi
80K
HE0206,80K
0 0.2V1V λt=16.5μm 0.0
4 8 12 16 4 8 12 16
3 6 9 12 Wavelength(μm)
Wavelength(μm)
FIG.3. (cid:2)Coloronline(cid:3)(cid:2)a(cid:3)Spectralresponseofdetectorswithvariedthresh-
FIG. 2. (cid:2)Color online(cid:3) The 80 K responsivity spectra of SP1 at different old wavelengths (cid:2)(cid:4)(cid:3). The curves from top to bottom are measured at the
bias.Theinsetshowsacomparisonwithmodeledresponsivity(cid:2)dashedline(cid:3) t
bias of 8V, 2V, 1V, and 2V, respectively. In comparison with the FCA
at 0.2Vbias with FCAcontribution alone. Peaks indicated by arrows are response (cid:2)dashed line(cid:3) calculated for the detector 1332, lh-hh transitions
interference modes of the cavity, which consists of p-GaAs/AlGaAs peri- produceresponsebetween4–10 (cid:2)m.(cid:2)b(cid:3)High-operating-temperaturecapa-
odiclayers.TheportionabovetheFCAcurveisascribedtoIVBAcontri-
bilitywasmeasuredonsamplesSP1,SP2,andSP3under0.2V,0.3V,and
bution,specificallythelh-hhtransitionsfor4–8 (cid:2)mrange. 3V,respectively,showingbroadrangefrom4–16.5 (cid:2)m.Thewavelength
regionabovedesignedthresholdisduetoathermaldetectionmechanism.
be verified from absorption spectra as shown in Fig. 1(cid:2)b(cid:3) Cavityinterferencemodesareallmarkedwiththearrowsin(cid:2)a(cid:3)and(cid:2)b(cid:3).
with theoretical FCA curves (cid:2)from transitions occurring
withinthesameband(cid:3)calculatedforcomparison.TheIVBA
different bias. Generally, the photoemission process deter-
appearsasontopofFCAlines,wherethebroadpeakaround
mines the escape rate of holes out of the emitter region fol-
4–16 (cid:2)m is due to the lh-hh transitions. Hole transitions lowing an escape cone model.9 However, with increasing
neartheBZcentercontributetothelong-wavelengthportion,
bias, the thermal assisted tunneling contribution will mix in
such as the transition (cid:2)3(cid:3) corresponding to absorption at
this process deteriorating the model accuracy, which can be
9 (cid:2)m.Although holes occupying the hh band reduces with
increasing k, the joint density of states (cid:2)JDOS(cid:3) (cid:8)k(cid:2)·(cid:4) (cid:2)E seen from the increasing threshold wavelength with bias.
k ki Therefore, the FCAresponsivity alone was calculated using
−Ekj(cid:3)(cid:8)−1 (cid:2)i and j represent band indexes(cid:3) showing singulari- theescapeconemodel9forabiasupto1Vunderwhichthe
ties due to the parallel feature of lh and hh bands results in
internal work function is nearly unchanged and taken from
considerable absorption in the short-wavelength range.
theArrhenius plot based on dark current measurements. Re-
Those transitions can take place in the (cid:6)111(cid:7)(cid:2)(cid:5)(cid:3) and (cid:6)100(cid:7)
sults show an agreement of measured responsivity with the
(cid:6)(cid:2)(cid:3)(cid:3) directions as indicated by arrows (cid:2)1(cid:3) and (cid:2)2(cid:3). Such an
FCA model curves in the long-wavelength portion and one
absorption feature is promising for infrared detection since
comparison is plotted in the inset of Fig. 2. When the FCA
bothMWIRandLWIRrangescanbecoveredusingasingle
dominates over the IVBA at longer wavelength, a good
p-GaAs based structure. matchingcanbeobtainedwhichisshowninFig.3(cid:2)a(cid:3).Simi-
Detector structures with varied emitter doping and (cid:4),
t lar FCA response pattern will be expected for higher-bias
demonstrating the lh-hh response, were grown on semi-
operation at which tunneling effects become prominent.The
insulating GaAs substrates. Sample HE0206 consists of
lh-hh transitions thus have the primary contribution to spec-
16 periods of 18.8 nm p-GaAs emitters doped to 1
tral response in the 4–8 (cid:2)m range in which the short-
(cid:6)1017 cm−3 and 125 nm undoped Al Ga As barriers.
0.12 0.88 wavelength response coincides with the absorption curves
Sample1332has12periodicunitswiththesamethickemit-
(cid:4)Fig. 1(cid:2)b(cid:3)(cid:5) approaching 4 (cid:2)m, while the long-wavelength
tersandbarriersasHE0206buttheemitterdopinglevelisat
3(cid:6)1018 cm−3 and theAl fraction of barriers is 0.15. Except portion is affected by the threshold wavelength. Two peaks
determined by their center positions at 5.50 (cid:2)m and
for theAl fraction, SP1, SP2, and SP3 have same layer pa-
rameters with 30 periods of 18.8 nm-thick 3(cid:6)1018 cm−3 6.46 (cid:2)m,respectively,canberesolved.Theircorresponding
energy values (cid:2)0.225 V and 0.192 eV, respectively(cid:3) agree
p-doped GaAs and 60 nm thick undoped Al Ga As where
x 1−x well with reported lh-hh separations along the (cid:5) and (cid:3) di-
x=0.28, 0.37, and 0.57, respectively. The so-hh transition-
based short-wavelength response in samples SP1(cid:9)3 have rections, e.g., (cid:3)1(cid:2)(cid:5)(cid:3)=0.224 eV in Ref. 10 and (cid:3)0(cid:2)(cid:2)(cid:3)(cid:3)
been previously reported and discussed.2The (cid:4) of HE0206, =0.193 eVinRef.11.Therefore,holetransitionsatpointsin
1332 and SP1(cid:9)3 at 16.5(cid:7)0.5 (cid:2)m, 15.t0(cid:7)0.3 (cid:2)m, k(cid:2)space along the (cid:5) and (cid:3) directions (cid:4)named (cid:2)1(cid:3) and (cid:2)2(cid:3) in
9.3(cid:7)0.3 (cid:2)m, 6.5(cid:7)0.3 (cid:2)m, and 4.1(cid:7)0.2 (cid:2)m, respec- Fig. 1(cid:2)a(cid:3), respectively(cid:5) are the reason for this result.Ahole
tively,arereferredtooperatingconditionslistedinFig.3(cid:2)a(cid:3). escaping over the potential barrier needs to undergo a pho-
Spectral response was measured on devices with the active toemission process at the emitter-barrier interface during
area of 260(cid:6)260 (cid:2)m2 by using a Perkin-Elmer system which its kinetic energy is required to be higher than the
2000FourierTransformInfraRed(cid:2)FTIR(cid:3)spectrometer.Abo- barriers following an escape cone in the momentum space.
lometer with known sensitivity is used for background mea- Differentphotoemissionratecanberesultedintermsofthek
surements and calibrating the responsivity of detectors. pointsonthelhbandontowhichholesareexcited,leadingto
Figure 2 shows the 80 K spectral responsivity of SP1 at the resolved (cid:3) and (cid:3)(cid:2) peaks in Fig. 2.
1 0
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091104-3 Laoetal. Appl.Phys.Lett.97,091104(cid:3)2010(cid:2)
TABLEI. ListofIVBAresponsepeaksforfourdetectorstructuresat80K The calculated specific detectivities (cid:2)D(cid:2)(cid:3) for SP1 and
excepttheSP3whichisobtainedat330K.Peaksaredeterminedthrough SP2atpeakresponsewavelengthsandoperatingat80Kand
their center positions. Different types of IBVAtransitions are indicated in 1 V bias by using the previously described methods2 are
Fig.1(cid:2)a(cid:3).
3.0(cid:6)107 and 1.5(cid:6)109 Jones, respectively. Performance op-
Transitionwavelengths timization is also possible by improving emitter absorption
(cid:2)(cid:2)m(cid:3) withhigherdopinglevels(cid:4)Fig.1(cid:2)b(cid:3)(cid:5).However,thescattering
(cid:4)t Emitterdoping effect12 is another factor needed to be considered for a final
Sampleno. (cid:2)(cid:2)m(cid:3) (cid:2)cm−3(cid:3) so-hh lh-hh(cid:2)1(cid:3) lh-hh(cid:2)2(cid:3)
optimization. The lh-hh transition-based concept presented
HE0206 16.5(cid:7)0.5 1(cid:6)1017 3.26 4.82 6.45 in this paper builds up the factors including the split-off
1332 15.0(cid:7)0.3 3(cid:6)1018 3.23 5.50 6.46 mechanism and the FCAfor GaAs being a platform to real-
SP1 9.3(cid:7)0.3 3(cid:6)1018 3.19 5.50 6.46 izemulti-spectralinfrareddetectioninaninternalphotoemis-
SP2 6.5(cid:7)0.3 3(cid:6)1018 3.20 5.47 6.45 sion detector. In comparison with MCT detectors4 which
SP3 4.1(cid:7)0.2 3(cid:6)1018 3.20 5.45 6.47 have been realized for uncooled operation within the
2–16 (cid:2)mspectralrangeandarecommerciallyavailable,the
discussed GaAs-based device will be a viable alternative
Developing detectors in the 4–8 (cid:2)m range is useful
with the robustness of the III-V material system. Uncooled
for short-range detection of bright infrared sources such as
operation is also possible for this type of device which can
the proximity fuze that is designed to detonate an explosive
be promising for some special applications such as high-
device. By using GaAs-based alloys such as GaAsP
intensity detection.
(cid:2)(cid:3) (cid:2)GaP(cid:3)=0.08 eV(cid:3)orGaAsSb(cid:2)(cid:3) (cid:2)GaSb(cid:3)=0.76 eV(cid:3),ex-
so so
tension of response range to either longer or shorter wave- This work was supported in part by the U.S.Army Re-
length is possible as (cid:3)1 roughly follows the (cid:2)2/3(cid:3)(cid:3)so rule. search Office under Grant No. W911NF-08-1-0448 moni-
These characteristics will facilitate the realization of multi- tored by Dr. William W. Clark, and in part by the U.S. Na-
spectral detection on a single GaAs-based detector. tional Science Foundation under Grant No. ECS-0553051.
According to Fig. 1(cid:2)b(cid:3), lh-hh absorption processes can AuthorsacknowledgeGreggoryRothmeierforhelpinmanu-
result in a spectral response longer than the response ob- script preparation.
tained from detector SP1. The long-wavelength capability
was investigated in detectors with varied doping levels and 1A.G.U.Perera,S.G.Matsik,P.V.V.Jayaweera,K.Tennakone,H.C.
(cid:4) as shown in Fig. 3(cid:2)a(cid:3).Acomparison with the model FCA Liu,M.Buchanan,G.VonWinckel,A.Stintz,andS.Krishna,Appl.Phys.
t
response was made on detector 1332 operating at 1 V bias, Lett. 89,131118(cid:2)2006(cid:3).
indicatinglh-hh transitionscanproducespectralresponseup 2P.V.V.Jayaweera,S.G.Matsik,A.G.U.Perera,H.C.Liu,M.Buchanan,
to 10 (cid:2)m. The lh-hh IVBA process is rather prominent in andZ.R.Wasilewski,Appl.Phys.Lett. 93,021105(cid:2)2008(cid:3).
3W.Songprakob,R.Zallen,D.V.Tsu,andW.K.Liu,J.Appl.Phys. 91,
terms of similar responsivity features observed in detector 171(cid:2)2002(cid:3).
HE0206 although its emitters are relatively low doped at 4A.Rogalski,Rep.Prog.Phys. 68,2267(cid:2)2005(cid:3).
1(cid:6)1017 cm−3.Asummarization of observed peaks is listed 5H.SchneiderandH.C.Liu,SpringerSeriesinOpticalSciences(cid:2)Springer,
in Table I. High-operating-temperature capability was mea- NewYork,2007(cid:3),Vol.126.
sured on detectors SP1, SP2, and SP3 as shown in Fig. 3(cid:2)b(cid:3), 6G. Ariyawansa, A. G. U. Perera, G. Huang, and P. Bhattacharya, Appl.
Phys.Lett. 94,131109(cid:2)2009(cid:3).
indicating promising uncooled operation. The range above 7H.S.Kim,E.Plis,A.Khoshakhlagh,S.Myers,N.Gautam,Y.D.Sharma,
(cid:4)t could be due to the thermal detection mechanisms.12 L.R.Dawson,S.Krishna,S.J.Lee,andS.K.Noh,Appl.Phys.Lett. 96,
Thermal-relatedprocessessuchasphononscatteringincrease 033502(cid:2)2010(cid:3).
the response time at high temperatures at which enhanced 8F.R.Giorgetta,E.Baumann,M.Graf,Q.Yang,C.ManzK.Köhler,H.E.
Beere,D.A.Ritchie,E.Linfield,A.G.Davies,Y.Fedoryshyn,H.Jäckel,
responsivity was observed by using a lower optical-path-
difference (cid:2)OPD(cid:3) velocity of the FTIR. A minimum OPD M10.39Fi(cid:2)s2c0h0er9,(cid:3).J. Faist, and D. Hofstetter, IEEE J. Quantum Electron. 45,
velocitybelowwhichresponseisnearlyunchangedwasthus 9D.G.Esaev,M.B.M.Rinzan,S.G.Matsik,andA.G.U.Perera,J.Appl.
employed. The peak at (cid:9)13 (cid:2)m is due to the cavity Phys. 96,4588(cid:2)2004(cid:3).
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found that the (cid:3) and (cid:3)(cid:2) peaks are almost fixed over the Rev.B 35,9174(cid:2)1987(cid:3).
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