sensors InAs/InAsSb Strain-Balanced Superlattices for Longwave Infrared Detectors Article

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1 snsors Articl Stra-Balancd Suprlattics Longwav Infrard Dtcrs Ttiana Manyk, *, Krystian Michalczwski,2, Krzyszt Murawski, Piotr Martyniuk Jaroslaw Rutkowski Institut Applid Physics, Military Univrsity Tchnology, 2 Urbanowicza Str., -98 Warsaw, Pol; krystian.michalczwski@wat.du.pl (K.M.); krzyszt.murawski@wat.du.pl (K.M.); piotr.martyniuk@wat.du.pl (P.M.); jaroslaw.rutkowski@wat.du.pl (J.R.) 2 VIGO Systm S.A. 29/33 Poznanska Str., 5-85 Ozarow Mazowicki, Pol; kmichalczwski@vigo.com.pl * Corrspondnc: ttjana.manyk@wat.du.pl; Tl.: Rcivd: 9 March 29; Accptd: 2 April 29; Publishd: 22 April 29 Abstract: typ-ii suprlattics (T2s) grown on a GaSb buffr layr GaAs substrats wr ortically vstigatd. Du stability at high opratg tmpraturs, T2s could b usd dtcrs opratg longwav frard (LWIR) rang diffrnt snsors clud,.g., CH 4 C 2 H 6 dtction, which is vry rlvant halth condition monirg. ortical calculations wr carrid out by 8 8 k p mthod. stimatd lctrons havy hols probability distribution a suprlattic () shows that wav function ovrlap crass whil thicknss dcrass. chang lctrons hols thicknss k z -dirction Brillou is shown. structurs a lowr than 5 nm ar mor optimal construction LWIR dtcrs basd on s. xprimntal rsults T2s bgap wr found b comparabl ortical on. propr fittg ortically calculatd xprimntally masurd spctral rspons charactristics trms a stra-balancd unbalancd structurs is shown. Kywords: T2s ; bgap; frard dtcrs; LWIR. Introduction Smith t al. [] 987 proposd us typ-ii suprlattics (T2s) InAs/GaSb as oplctronic matrials xhibitg xcllnt lctro-optical proprtis, ortically comparabl HgCdT bg ma compound dtction frard radiation (IR) rgion [2]. In addition, Ga-fr T2s InAs/InAs x Sb x hav bn provd hav a longr carrir liftim (τ) than InAs/GaSb T2s [3] hav bn proposd as an altrnativ IR phodtcrs [4]. molcular bam pitaxy (MBE) tchnology dvlopmnt allowd vstigation suprlattics (s) on a GaSb buffr layr grown on GaAs substrats. InAs x Sb x bgap (E g ) changs non-larly Sb molar composition trnary compound. m this rlation dpnds on InAs x Sb x growth mthod is givn diffrnt ms by rsarch groups [5,6]. In s du T2s b alignmnt lctron hol stats ar confd InAs (lctrons) InAsSb (hols) layrs, thus lctrons hols ar spatially sparatd. r, by adjustmnt InAs /or InAsSb thicknss as wll as Sb molar composition (x Sb ), it is fasibl tun E g a wid rang IR. Owg s uniqu proprtis, T2s hav bn chosn as matrials applications longwav frard radiation (LWIR) dtcrs opratg 8 5 µm rang. Both phoconductiv phovoltaic Snsors 29, 9, 97; doi:.339/s9897

2 that clud risg potntially unsustaabl halth car costs, maly du crasg prvalnc chronic disass, flunc on halth xtrnal nvironmntal facrs cludg climat chang, r is a nd hav simpl dvics allowg us dtct diagnos.g., lipid proxidation, vitam E dficincy, chronic rspirary disas, clls oxidativ strss, Snsors 29, or 9, vn 97sclrodrma cystic fibrosis. This could b allowd by.g., 2 C2H6 lvl monirg through unxplord LWIR, rquirg a propr dtcr opratg that rang. In addition, dtcrs ar constructd. LWIR, T2s two ma dtrimntal ar maly scattrg usd ffcts fabrication Rayligh barrir dtcrs Mi ar significantly clud nbn rducd pbn [2,3]. dsign [7,8], low-nois trb cascad frard phodtcrs (ICIP) [9,], dual b T2 long-wavlngth systm was frard modld phodiods usg a varity [] vry ortical fast avalanch approachs, phodiods such as (APD). tight-bdg, s dtcrs psudopotntial can b usd a wid k p rang mthods. applications k p mthod filds is widly scinc, usd mdic, bcaus safty, its propr dustry, numrical aumotiv, accuracy. such W as railway prsnt safty, a comparison gas lak dtction, rsponsivity flam dtction, hat high distribution opratg tmpratur monirg, mdical (HOT) diagnostic LWIR InAs/InAs xsbx imagg, spac oprations, T2s phoconducrs night vision dvics simulatd spctroscopy. Sc spctra. humanity is facg halthcar challngs that clud risg potntially unsustaabl halth car costs, maly du crasg prvalnc chronic disass, flunc on halth 2. Matrials Mthods xtrnal nvironmntal facrs cludg climat chang, r is a nd hav simpl dvics allowg ortical us dtctcalculation diagnos b.g., lipid structur, proxidation, Eg vitam E cofficint dficincy, (α) chronic was rspirary prmd usg disas, clls stard oxidativ k p (8 strss, 8 mthod) or vnby sclrodrma SimuApsys cystic nxtnano fibrosis. This platms could[4,5]. b allowd In by.g.,, schmatic C 2 H 6 lvlrprsntation monirg through unxplord bs LWIR, rquirg strad a propr unstrad dtcr opratg that is prsntd. rang. In addition, LWIR, two ma dtrimntal scattrg ffcts Rayligh Mi ar significantly rducd shows [2,3]. that whn is cohrntly strad, all paramtrs ar bg changd T2 clud systmconduction was modld b usg fst a varity (CBO), ortical valnc b approachs, fst (VBO) such as Eg tight-bdg, InAs (InAsSb) psudopotntial layrs. k p blu mthods. l corrsponds k p mthod lowst is widly conduction usd bcaus b (CB), its propr numrical rd l dicats accuracy. W highst prsntvalnc a comparison b (VB). If rsponsivity lattic-match high opratg GaSb tmpratur substrat (HOT) is takn LWIR account, InAs/InAs x InAs Sb x T2s InAs xsbx phoconducrs layrs bcom simulatd strad valnc spctra. b splits havy (hh) light () hol sub-bs s. In violt l rprsnts subb 2. Matrials dg Mthods strad s sparation hh bs is also visibl. chang ortical VBO valu calculation btwn stat bout structur, stra E g strad rmas cofficint (α). was V prmd [6]. usg k p stard (8 8 k p mthod) (8 8 mthod) simulation by was SimuApsys implmntd nxtnano study disprsion platms [4,5]. curvs In ordr, stimat schmatic s rprsntation. ic bs boundary strad conditions wr unstrad usd simulation procdur. is prsntd. s conditions impos icity on wav functions (WF).. Schmatic rprsntation unstrad strad typ-ii suprlattics. Schmatic rprsntation unstrad strad typ-ii suprlattics (T2s) (T2s) InAs/InAs xsbx s. InAs/InAs x Sb x s. shows that whn is cohrntly strad, all paramtrs ar bg changd clud conduction b fst (CBO), valnc b fst (VBO) E g InAs (InAsSb) layrs. blu l corrsponds lowst conduction b (CB), rd l dicats highst valnc b (VB). If lattic-match GaSb substrat is takn account, InAs InAs x Sb x layrs bcom strad valnc b splits havy (hh) light () hol sub-bs s. In violt l rprsnts subb dg strad s sparation hh bs is also visibl. chang VBO valu btwn stat out stra strad rmas. V [5]. k p (8 8 mthod) simulation was implmntd study disprsion curvs ordr stimat s. ic boundary conditions wr usd simulation procdur. s conditions impos icity on wav functions (WF).

3 Snsors 29, 9, 97 3 paramtrs InAs, InSb GaSb layrs usd InAs/InAs x Sb x s simulation procdur ar prsntd Tabl. Paramtrs ar takn from paprs svral authors [5,6 2]. E g tmpratur (T) is givn by Varshni m: E g (T)= E αt 2 /(T + β). Tabl. Matrial paramtrs InAs, InSb GaSb layrs usd simulation. Paramtr InAs InSb GaSb E (Γ) [V] E (X) [V] E (L) [V] so [V] m /m (K) E v, vac a = f (T) [Å] (T 3) (T 3) (T 3) All paramtrs trnary compounds usd simulations wr stimatd basd on bulk paramtrs bary compounds. It should b notd that w considrd symmtrical cas whn Kan paramtr, F = [5]. Most paramtrs assumd simulations xhibit T dpndnc vary larly x Sb. In ordr calculat som InAs x Sb x ( < x Sb < ) paramtrs bowg shown Tabl 2 was usd. Tabl 2. Bowg paramtr assumd simulations (T = 23 K). Bowg Cofficint Bowg Paramtr (b bow ) b g [V].72 b so [V].2 b m/m.35 b v, vac [V].47 An quation trnary compounds paramtrs, Y InAsSb dpndnc on bowg cofficint is dfd as: Y InAsSb = ( x Sb ) Y InAs + x Sb Y InSb b bow x Sb ( x Sb ). () Luttgr paramtrs hav bn stimatd basd on rspctiv accordg quations prsntd by Birnr t al. [5] Vurgaftman t al. [6]. VBO was dtrmd by followg quation: VBO = E v,vac(inas) [ E v,vac(inas) ( x Sb ) + E v,vac(insb) (x Sb ) x Sb b v,vac ( x Sb ) ], (2) whr vacuum lvls valnc b (E v, vac ) valnc b bowg paramtr (b v, vac ) wr prsntd Tabls 2, rspctivly. All calculatd structurs ar stra-balancd on GaSb. stra-balancd condition is rachd by sttg avrag lattic paramtr on wightd layr thicknss bg qual lattic constant GaSb. InAs x Sb x layr thicknss (d InAsSb ) x Sb, lattic constant (a InAs(InSb, GaSb) ) (L) can b calculatd from Equation [22]: ( ) agasb a d InAsSb = InAs L. (3) a InSb a InAs x Sb lattic constant at 3 K is prsntd Tabl. thicknss InAsSb layr structurs was dtrmd by rlation (3) givg thicknss layr bg compnsatd zro sum stras all constitunt layrs.

4 Snsors 29, 9, x 4 Snsors 29, 9, x 4 Snsors 29, 9, Rsults Discussion 3. Rsults Discussion 3.. Influnc Priod on Suprlattic () Paramtrs 3. Rsults Discussion 3.. Influnc 2 shows Priod on lowst Suprlattic () Paramtrs (Eg-btwn first lvl CB VB hh) 3.. Influnc xsb 2 InAsSb shows Priod on lowst s Suprlattic btwn () nm Paramtrs (Eg-btwn 4 nm at T = first 23 K. lvl CB VB hh) xsb 2 InAsSb dpicts shows that lowst it s is possibl btwn rach (E nm dsird g -btwn 4 nm Eg by at first T changs = lvl 23 K. both xsb L. Whn xsb CB VB hh ) L x Sb cras, InAsSb 2 dpicts Eg dcrass. s that it is btwn possibl nm rach 4 dsird Eg nm at T = 23 by changs K. both xsb L. Whn xsb L cras, Eg dcrass. 2. ortically simulatd Eg stra balancd suprlattic () structurs 2. xsb 2. ortically at T = 23 K. simulatd EEg g stra balancd suprlattic () structurs xxsb at T = 23K. brokn l 2 dicats an qual. V, which allows us compar diffrnc brokn btwn 2 dpicts l that thicknss it is possibl 2 dicats rach an dsird qual stra-balancd E g by. changs V, which structurs both allows x Sb us compar L. Whn sam x Eg. Sb diffrnc L cras, btwn E g cofficint dcrass. thicknss prsntd 3 was stra-balancd calculatd by structurs commrcial SimuApsys sam Eg. platm brokn accordg l cofficint mthod prsntd 2 dicats prsntd an [24] 3 was qual slctd calculatd.pots V, which by from allows this commrcial l us compar SimuApsys anor diffrnc. platm accordg btwn thicknss mthod prsntd [24] stra-balancd slctd pots from structurs this l anor sam E g.. 3 shows cofficint that α prsntd nar dg 3 was calculatd dcrass by whn commrcial thicknss SimuApsys platm accordg crass, 3 bg shows mthod connctd that prsntd α nar dg [23] ovrlap slctd lctrons pots dcrass from whn this hols l thicknss WF anor.. crass, bg connctd ovrlap lctrons hols WF α ortical ortical simulation simulation phon phon stra-balancd stra-balancd.. 3 shows 3. α ortical that α nar simulation dg phon dcrass stra-balancd whn thicknss. probability distribution lctrons havy hols InAsSb/InAs s is prsntd crass, bg connctd ovrlap lctrons hols WF. 4. s probability simulations distribution ar at T = lctrons 23 K xsb = havy.38 hols InAsSb/InAs L = 2 nm, s 2 nm is prsntd 29 nm, probability distribution lctrons havy hols InAsSb/InAs s is prsntd rspctivly. 4. s simulations havy hol ar WF at is T strongly 23 localizd xsb.38 InAsSb barrir 2 nm, rgion 2 nm but lctron 29 nm, 4. s simulations ar at T = 23 K x WF rspctivly. sprads out through havy hol structur WF is strongly significant Sb =.38 L = 2 nm, 2 nm 29 nm, localizd probability InAsSb rsidg barrir rgion InAs but quantum lctron rspctivly. havy hol WF is strongly localizd InAsSb barrir rgion but lctron WF wll WF sprads (QW) rgion. out through 4 shows structur that if significant probability rsidg stra-balancd InAs crass quantum sprads out through structur significant probability rsidg InAs quantum wll wll ovrlap (QW) rgion. lctrons 4 shows hols, that if WF dcrass. valus stra-balancd ovrlap ar 2.4%, crass 4.8%, (QW) rgion. 4 shows that if stra-balancd crass 8.7% ovrlap lctrons L = 2 nm, hols, 2 nm, WF 29 dcrass. nm, rspctivly. valus dcras ovrlap ovrlap ar 2.4%, confirms 4.8%, ovrlap lctrons hols, WF dcrass. valus ovrlap ar 2.4%, 4.8%, 8.7% rduction 8.7% α whn L = 2 nm, crass. 2 nm, 29 nm, rspctivly. dcras ovrlap confirms L = 2 nm, 2 nm, 29 nm, rspctivly. dcras ovrlap confirms rduction rduction α whn crass. α whn crass.

5 Snsors 29, 9, 97 Snsors 29, Snsors 29, 9, 9, xx (c) (c) 4.4.Elctrons Elctrons havy havyhols holsprobability probabilitydistribution distribution structurs 23 K structurs at at Elctrons havy hols probability distribution structurs at K23 K : : nm; 2 nm; nm; 2 nm; (c)nm. 29 nm. 2 2 (c) 29 : 2 nm; 2 nm; (c) 29 nm. Th structurs structurs shows shows that bttr optical optical proprtis Th proprtis thnr thnrlayrs layrs Th structurs shows that bttr optical proprtis thnr layrs ar mor stabl trms lctrons hols traction dpr lvls. As ar mor stabl trms lctrons hols traction dpr lvls. Ascan can ar mor stabl trms lctrons hols traction dpr lvls. As can bsn snfrom from 5,5,whn whn is is abov abov 5 nm, position b position hh hh sub-bs sub-bsisis b sn from 5, whn is abov 5 nm, position hh sub-bs is changdaffctg affctgon onα.α.in In aa xcdg xcdg3 3 nm nm thr thr bs bs havy havy hols: hh,, hh changd hh22 changd affctg on α. In a xcdg 3 nm thr bs havy hols: hh, hh2 hh 3 lis abov light hol sub-b. hh3 lis abov light hol sub-b hh3 lis abov light hol sub-b. 5. CB VB: hh, hh2, hh3, positions CBCB VB: VB:hhhh, hh hh3,3, positions positions..,hh 2,2,hh lctrons hols wr calculatd from disprsion curvs as lctrons hols wr(k). calculatd from as scond drivativ lctrons hols wr from curvs as scond by wav vcr Forcalculatd disprsion kx, disprsion ky curvs Brillou drivativ by wav vcr (k). For k, k Brillou x y scond drivativ by wav vcr (k). For k x, k y Brillou hardly chang but dirction kz dpndnc hardly chang but dirction k dpndnc z hardly 6). butwhn dirction kz dpndnc chang is significant (s xsb crass hh iswhil significant (s 6). Whn xsb crass hh whil both issignificant (s Whn xsban crass hh dcrass both cras. It can 6). b sn that cras dcrass dcrass cras. It can b sn that an cras lads mor whil both cras. It can b sn that an cras lads mor significant chang mass. Morovr, it should b notd that a significant significant mass. Morovr, should b mass notd that a chang chang it mass. Morovr, it should bstays notd that chang lads chang mor rang 2 nm, slowly crass constant a rang 2 nm, mass slowly crass.m constant a furr whil chang a rang nm, stays massconstant slowly crass similar stays.m whil furr cras 2 thos cras bcom hh cras thos cras bcom similar hh..m whil a furr cras thos cras bcom similar hh. InIn LL == nm nmat attt==23 23K, K, calculatd calculatd.62 cas cast2s T2sInAs/InAs InAs/InAs.62Sb Sb * =,, hh kkxx,, k ( ) knm ( ) Brillou ar: ar:m m cas hh.38 kyy ( ) zz ( ) Brillou In T2s InAs/InAs.62Sb L = 4.5k at T = 23 K, calculatd = * =.23m, m * =.4m, m * = 3.2m, m * =.4m, m * =.96m..9m, m.9m,m =.23m, m =.4m, m 3.2m, m =.4m, m., hh,k y ( ) k z ( ) Brillou ar: m* = hh hh hh hh kx= =.96m.9m, m* =.23m, m*hh =.4m, m*hh = 3.2m, m* =.4m, m* =.96m.

6 Snsors 29, 9, x Snsors 29, 9, 97 Snsors 29, 9, x calculatd hh, hh2, hh3 kz-dirction hh, hh Brillou. 2, 2hh 3 3 calculatd calculatd hh, hh, hh kzk-dirction z-dirction Brillou. Brillou. In ordr xpla shap curvs a widr phon rang, it is In ordr considr xpla shap curvs a widr phonα rang, it is ncssary light [25]. 7 shows both transvrs In ordr xpla shap curvs a widr phon rang, it is ncssary considr light [24]. 7 shows α both transvrs lctronic lctronic (TE) transvrs magntic (TM) mod LWIR rgion two diffrnt s ncssary considr light [25]. 7 shows α both transvrs (TE) transvrs magntic mod LWIR rgion two show diffrnt s qual qual L(TE) = 4.5 L (TM) = magntic 25 nm. s calculations lctronic nm transvrs (TM)ortical mod LWIR rgion four two promnt diffrnt s L =channls, 4.5 nm L = 25 nm. s ortical calculations show four promnt channls, -hh -hh 3 ortical - contributg TE this qual L =namly 4.5 nm, L=-hh 252, nm. s calculations show four TM promnt namly -hh, rgion. -hh2, -hh is TE TM this wavlngth 3 -strngth contributg wavlngth TE highr than that TM. channls, namly -hh, -hh2, -hh3 - contributg TE TM this rgion. strngth TE is highr than that TM. wavlngth rgion. strngth TE is highr than that TM. 7. -dpndnt transvrs lctronic (TE) transvrs magntic (TM) 7. -dpndnt transvrs lctronic (TE) transvrs magntic (TM) α α InAs/InAs.62 Sb.32 structurs at 23 K qual :magntic 4.5 nm, 7. -dpndnt transvrs lctronic (TE) transvrs (TM) InAs/InAs.62 Sb.32 structurs at 23 K qual : 4.5 nm, 25 nm. nm. InAs/InAs.62Sb.32 structurs at 23 K qual : 4.5 nm, α25 probability is proportional squar optical lmnt pr. probability is proportional squar optical lmnt pr. 25 nm. 8 prsnts optical lmnts -hh, -hh 2,-hh -hh 3-8 prsnts optical lmnts, -hh - probability is proportional squar pr. -hh 2, optical 3 lmnt TE InAs/InAs.62Sb.32 stra-balancd L = 25 nm at T = 23 K. 8 TM prsnts optical lmnts -hh, -hh 2, -hh 3 - TE TM InAs/InAs Sb stra-balancd L = 25 nm at T = 23 K optical lmnt -hh is largr TE than TM. In turn, TEoptical TM.62Sb.32 stra-balancd Lthan = 25 nmtm. at TIn= turn, 23 K. lmnt InAs/InAs -hh is largr TE optical TE-polarizd nar Eg du -hh, TM lmnt crass -hh sharply is largr TE than whil TM. In turn, TE-polarizd crass sharply nar Eg du -hh, whil TM

7 Snsors 29, 9, 97 7 Snsors 29, 9, 9, x 7 TE-polarizd crass sharply nar E g du -hh, whil TM crass markdly at at highr nrgis du shows that optical lmnt -hh2 -hh2 2 has no ffct on cofficint α, α, sc its valu is is almost zro TE TM polarizd optical InAs/InAs.62Sb.32 InAs/InAs.62Sb.32 stra 8. TE TM polarizd optical InAs/InAs.62 Sb.32 stra balancd balancd L = 25 nm at at T = 23 K. L = 25 nm at T = 23 K. Typical spctra contas two ma faturs whr on is is an cras (-hh) whil scond Typical on spctra is is a pak contas at at highr two ma faturs corrspondg whr on is an cras btwn or ( bs. -hh ) whil From scond ortical on is dscriptions a pak at highr prsntd abov, corrspondg it it follows that two s btwn hav a or grat bs. flunc From on α, α, namly -hh -hh ortical dscriptions - - prsntd (s abov, 7). it follows that two s hav a grat flunc on α, namly -hh - (s 7) Comparison ortical Simulation Exprimntal Data 3.2. Comparison T2s ortical Simulation wr grown on Exprimntal GaAs substrats Data by a RIBER Compact 2-DZ solid-sourc T2s MBE systm. A wr.2 μm-thick grown on GaSb GaAs layr substrats was grown by a RIBER rduc Compact larg 2-DZ lattic solid-sourc mismatch MBE btwn systm. GaAs A substrat.2 µm-thick GaSb s. layr n, was grown 3 s rduc 34.3 ML larg InAs/9 lattic ML mismatch InAsSb s btwn wr GaAs dpositd. substrat Growth dtails s. n, 3 s ar 34.3 rportd ML InAs/9 papr ML InAsSb by Michalczwski s wr dpositd. t t al. [26]. Growth Aftr dtails growth, pholithography-assistd ar rportd wt-tchg papr was by usd Michalczwski df t activ al. [25]. Aftr contact growth, aras pholithography-assistd IR phoconducrs. wt-tchg vacuum was vaporation usd df Au/Ti was activ applid contact fabricat aras ohmic IR contacts. phoconducrs. vacuum vaporation Au/Ti was applid fabricat ohmic contacts. In In ordr obta a a propr agrmnt btwn ortical calculations xprimntal data, tmpratur-dpndnt bowg paramtr EEg Eg g was was usd. In our simulation bowg paramtr dcrass T assumg.67 mv at at 3 3 K. K. 9 shows ortical simulation xprimntal data α.7.7 µm μm thick thick T2s T2s InAs/InAs InAs/InAs.62Sb.38 InAs/InAs.62Sb L = 3.2 nm at 3 K. W W hav hav rachd rachd propr propr agrmnt agrmnt btwn btwn xprimntal xprimntal data data ortical ortical simulation. simulation. 9 shows 9 shows -hh bg -hh -hh qual bg E g qual scond Eg Eg on corrsponds scond on corrsponds α α ortical simulation xprimntal data data T2s T2s InAs/InAs InAs/InAs.62Sb.38 InAs/InAs.62Sb.38 Sb.38 L = 3.2 L = nm 3.2 at nm T at = at 3 T = K. 3 K. K. T2s phoconducr spctral currnt rsponsivity (Ri) opratg LWIR rang at at bias.5 V T = 23 K was masurd rsults ar prsntd whr grn l dpicts

8 A B shows a comparison Ri ortical simulation xprimntal rsults two sampls. ir common fatur is sam composition (xsb =.38) whil diffrnc is thicknss s ( ratio thicknsss InAs InAsSb) Eg. a corrsponds Snsors 29, 9, 97 8 sampl-a whr thicknss is locatd stra-balancd rgion whil b dpicts sampl-b xhibitg unbalancd stra structur. fittg xprimntal rsults was prmd by τ. Tabl 3 dicats T2s phoconducr that τ sampl-b spctral is much currnt lowr rsponsivity than sampl-a (R i ) opratg xplag LWIR diffrnc rang at bias Ri..5W V bliv T = 23 that K was structur masurd by which rsults rsponsivity ar prsntdis prsntd whr grn a l is optimally dpicts ortical balancd. fittg Thus, whil optimal pk starsstructur corrspond T2s xprimntal rsults LWIR twophodtcrs sampls, A B. should hav, an stra-balancd thicknss InAs absorbr InAs x Sb x, xfollowg Sb, E g paramtrs: fittg τ ar prsntd 2 Tabl nm < 3. L < 5 nm Sb molar composition InAs-xSbx.37 < x <.45.. Ri ortical simulation xprimntal rsults T2s InAs/InAs.62Sb.38. R i ortical simulation xprimntal rsults T2s InAs/InAs.62 Sb.38 phoconducr sampl-a; sampl-b at T = 23 K. phoconducr sampl-a; sampl-b at T = 23 K. 4. Conclusions Tabl 3. sampl-a sampl-b paramtrs. T2s Sampl InAs/InAs-xSbx L [nm] Ls InAsSb on [nm] a GaSb buffr L InAs [nm] GaAs x Sb substrat E g [V] wr vstigatd. τ [ns] us InAs/InAs-xSbx A s 3.2 givs a grat 2.8 opportunity.4 fabricat.38 dvics.48 IR radiation 24 dtction a wid wav rang B by slctg Sb molar.38 composition.996 InAs-xSbx.2 barrir. In calculations, thicknss InAsSb barrir givn was assumd nsur a stra balancd s. papr shows that rduction thicknss cras Sb molar In cas ortical calculations R i was stimatd by α τ fittg. ortical composition InAsSb barrir allows highr b rachd sam calculations xhibit propr cocidnc xprimntal data. shows a comparison R i ortical simulation xprimntal rsults two sampls. ir common fatur is sam composition (x Sb =.38) whil diffrnc is thicknss s ( ratio thicknsss InAs InAsSb) E g. a corrsponds sampl-a whr thicknss is locatd stra-balancd rgion whil b dpicts sampl-b xhibitg unbalancd stra structur. fittg xprimntal rsults was prmd by τ. Tabl 3 dicats that τ sampl-b is much lowr than sampl-a xplag diffrnc R i. W bliv that structur by which rsponsivity is prsntd a is optimally balancd. Thus, optimal structur T2s LWIR phodtcrs should hav an stra-balancd absorbr followg paramtrs: 2 nm < L < 5 nm Sb molar composition InAs x Sb x.37 < x <.45.

9 Snsors 29, 9, Conclusions T2s InAs/InAs x Sb x s on a GaSb buffr GaAs substrat wr vstigatd. us InAs/InAs x Sb x s givs a grat opportunity fabricat dvics IR radiation dtction a wid wav rang by slctg Sb molar composition InAs x Sb x barrir. In calculations, thicknss InAsSb barrir givn was assumd nsur a stra balancd s. papr shows that rduction thicknss cras Sb molar composition InAsSb barrir allows highr b rachd sam dg. An improvmnt is causd by cras lctrons hols wav function ovrlap du thnr lowr InAsSb barrir. With chang thicknss, position light havy hol bs changs significantly. With a smallr than 5 nm, light hols b is locatd dirctly undr havy hols b, whil s largr than 3 nm it is sparatd from conduction b by thr havy hols bs. Numrical simulations show that position light hols sub-b dirctly blow first havy hols sub-b crass probability optical s, hnc structurs a smallr ar mor optimal construction LWIR dtcrs basd on s. xprimntal data wr compard rsults numrical simulations, showg propr agrmnt by liftim fittg. stimatd carrir liftim a balancd structur is mor than an ordr magnitud highr than a non-balancd on dicatg that gnration a larg numbr dfcts unbalancd structur crass rcombation rat carrirs rducg carrir liftim currnt rsponsivity. Author Contributions: Concptualization, T.M.; Mthodology, T.M.; Formal Analysis, J.R.; Invstigation, K.M. (Krystian Michalczwski) K.M. (Krzyszt Murawski); Writg-Origal Draft Prparation, T.M.; Writg-Rviw & Editg, P.M. J.R. T.M.; Projct Admistration, P.M. Fundg: This rsarch was fundd by grant numbr TECHMATSTRATEG/34775/5/NCBR/27. Conflicts Intrst: authors dclar no conflict trst. Rfrncs. Smith, L.D.; Maiiot, C. Proposal strad typ II suprlattic frard dtcrs. J. Appl. Phys. 987, 62, [CrossRf] 2. Rogalski, A.; Martyniuk, P.; Kopytko, M. InAs/GaSb typ-ii suprlattic frard dtcrs: Futur prospct. Appl. Phys. Rv. 27, 4, 334. [CrossRf] 3. Stnbrgn, E.H.; Connlly, B.C.; Mtcalf, G.D.; Shn, H.; Wraback, M.; Lubyshv, D.; Qiu, Y.; Fastnau, J.M.; Liu, A.W.K.; Eamri, S.; t al. Significantly improvd mority carrir liftim obsrvd a long-wavlngth frard III-V typ-ii suprlattic comprisd. Appl. Phys. Ltt. 2, 99, 25. [CrossRf] 4. Rogalski, A.; Kopytko, M.; Martyniuk, P. Antimonid-Basd Infrard Dtcrs: A Nw Prspctiv; SPIE Prss: Bllgham, WA, USA, Wbstr, P.T.; Riordan, N.A.; Liu, S.; Stnbrgn, E.H.; Synowicki, R.A.; Zhang, Y.-H.; Johnson, S.R. Masurmnt InAsSb bgap b dg positions usg spctroscopic llipsomtry pholumscnc spctroscopy. J. Appl. Phys. 25, 8, [CrossRf] 6. Svnsson, S.P.; Sarny, W.L.; Hir, H.; L, Y.; Wang, D.; Dontsky, D.; Shtrngas, L.; Kipshidz, G.; Blnky, G. B gap InAs x Sb x nativ lattic constant. Phys. Rv. B 22, 86, [CrossRf] 7. Kim, H.S.; Cllk, O.O.; L, Z.-Y.; H, Z.-Y.; Zhao, X.-H.; Liu, S.; Li, H.; Zhang, Y.-H. Long-wav frard nbn phodtcrs basd on typ-ii suprlattics. Appl. Phys. Ltt. 22,, 64. [CrossRf] 8. Haddadi, A.; Chn, G.; Chvallir, R.; Hoang, A.M.; Razghi, M. InAs/InAs x Sb x typ-ii suprlattics high prmanc long wavlngth frard dtction. Appl. Phys. Ltt. 24, 5, 24. [CrossRf] 9. Lotfi, H.; Li, L.; Y, H.; Hky, R.T.; Li, L.; Yang, R.Q.; Kay, J.C.; Mishima, T.D.; Sans, M.B.; Johnson, M.B. Intrb cascad frard phodtcrs long vry-long cutf wavlngths. Infrard Phys. Tchnol. 25, 7, [CrossRf]

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