among the group - iii nitrides , wurtzite inn ( w - inn ) is a very promising semiconductor material of application in high - frequency / high - speed / high - power heterojunction field - effect transistors ( hfets ) [ 1 - 4 ] , due to its superior electron transport properties , small effective mass , and high mobility . w - inn also has been used in field emitter because of its negative affinity ( net ) [ 5 - 7 ] . hexagonal boron nitride ( h - bn ) is a sp - bonded layered compound isostructural to graphite . due to its wide band gap there were several reports on field emission characteristics of h - bn films [ 8 - 10 ] . chinaru and his co - workers   designed an h - bn / gan field emission device , which appeared lower turning on voltage compared with the conventional devices . the band structures of w - inn and h - bn are very similar to that of h - bn and gan , so w - inn / h - bn is promising for field device . it is important to accurately determine the valence band offset ( vbo ) and conduction band offset ( cbo ) for using w - inn / h - bn - based electronic devices . theoretical and experimental values of band structure have been extensively investigated for the w - inn and h - bn , respectively , but it is still scarce for the w - inn / h - bn heterojunction . this letter reports the valence band discontinuity at the w - inn / h - bn heterojunction interface . three samples were used in our x - ray photoelectron spectroscopy ( xps ) experiments . a 40-nm - thick h - bn layer was deposited by ion beam assisted deposition on si substrate . w - inn films were deposited by metal organic chemical vapor deposition ( mocvd ) : a 5-nm - thick w - inn grown on a prepared h - bn layer on si substrate and a 250-nm - thick w - inn grown on si(111 ) substrate . the crystal qualities of w - inn were characterized using the high - resolution x - ray diffraction apparatus at beijing synchrotron radiation facility . the full width at half maximum of the x - ray diffraction rocking curve ( xrc ) is 0.75. the w - inn is unintentionally n - type doped , the carrier concentration is 1  10 cm determined by hall performed in single field the van der pauw geometry at room temperature . however , the h - bn is high resistance . xps measurement was performed on phi quantera sxm instrument with al k ( h = 1486.6 ev ) as the x - ray radiation source and the angle between the x - ray source and the detector is 45. the work function and the fermi energy level ( ef ) of the instrument had been carefully calibrated . the surfaces of all the samples were exposed in the air , so existence of impurities ( such as oxygen and carbon ) on the surface may prevent the precise determination of the valence band maximum ( vbm ) . in order to reduce the contamination effect , all the samples were subjected to surface clean procedure by ar bombardment with a voltage of 1 kv at a low sputtering rate of 0.5 nm / min . the total energy resolution of xps system is about 0.5 ev , and the precision of the binding energy is within 0.03 ev after careful calibration . all xps spectra were calibrated by the c 1-s peak at 284.8 ev from contamination to compensate the charge effect . the vbo can be calculated according to where   is the energy difference between in 3d5/2 and b 1s cls at the w - inn / h - bn interface . in the terms of   and ,   and are the cls of w - inn and h - bn bulk constants of thick films , respectively , and ,   means the bulk position of the valence band maximum with respect to the ef . the positions of valence band maximum ( vbm ) in valence band ( vb ) spectra are determined by linear extrapolation of leading edges of vb spectra to the base lines in order to account for the finite instrument resolution . since considerable fitted line to the original measured data has been obtained , the uncertainty of the cl positions should be lower than 0.03 ev , as evaluated by numerous fitting with different parameters . the in 3d5/2 spectra for w - inn and w - inn / h - bn samples , the b 1-s spectra for h - bn and w - inn / h - bn samples , and the valence band photoemission for both w - inn and h - bn samples are shown in fig . 1 . the parameters deduced from fig . 1 are summarized in table 1 for clarity . as illustrated in fig . 1a and 1e , the cl lineshapes of w - inn appeared a weak asymmetry . the intrinsic plasmon is that a strong local potential produced when an electron of cl was removed from the matrix , leaving a positive charge of photohole and then the deexcitation of the photohole by quantized excitations the conduction - electron system . however , the extrinsic plasmons are excited by the outgoing photoelectron traveling from the place of the photoexcitation process to the surface [ 14 - 17 ] . considering the couple of the surface plasmons and photoelectrons , the final - state is projected onto screened component and unscreened component . we attribute the lower energy component to the  screened  final - state and the higher - energy component to the  unscreened  final - state . wertheim and his co - worker   used this model to explain screening response in narrow band metal . the energy of the surface plasmon is   here n is the carrier concentration , ( ) and m are the high - frequency dielectric constant and the effective mass of the conduction electron , respectively . for the unintentionally doped n - type w - inn , the carrier concentration is much lower than that of metal . the energy of plasmon is always less than 1 ev , which is comparable with the intrinsic linewidth . the screened and unscreened peaks overlapped , resulting in an asymmetric core lineshape . the in 3d5/2 consists of three peaks by voigt fit using shirley background , the positions of peak locked at 443.71 , 444.54 , and 445.45 ev , as shown in fig . 1a . the binding energy of 443.71 and 444.54 ev associated with screened final state and the unscreened final states , respectively . the binding energy of 445.45 ev belongs to in - o bond . similarly , in the w - inn / h - bn system , the binding energy of 443.78 and 444.67 ev belong to screened and unscreen final states , respectively . according to previous reports , it is suggested that the energy 446.15 ev is in - o bonding in fig . cl spectra of in 3d5/2 recorded on w - inn bulk ( a ) and w - inn / h - bn ( e ) samples , b 1-s spectra on h - bn bulk ( c ) and w - inn / h - bn heterojunction ( f ) . samples , w - inn vb spectra ( b ) and h - bn vb spectra . all peaks have been fitted to voigt line shapes using shirley background , and the vbm values are determined by linear extrapolation of the leading edge to the base line parameters ( binding energy , full width at half maximum ( fwhm ) ) of the xps peaks and vbms for w - inn , h - bn and w - inn / h - bn samples , the spectra as shown in fig . 1 energy is referenced to the fermi level ( 0 ev).the errors in the peak positions and vbm are  0.03 and 0.08 ev , respectively the energy differences between the unscreened and the screened are 0.83 and 0.89 ev for the bulk and the heterojunction . bn 1-s peak in the bulk and heterojunction is 190.1 and 190.37 ev , respectively . the vbm lineshape and the cl positions of h - bn are very similar to the latest reports . due to the peak and linewidth of higher - binding energy ( unscreened final - state ) depend on the excitement of bulk , surface treatment , we choose the lower - binding energy components related to screened final - state for vbo calculation , in this letter . at room temperature , taniguchi and his coworker have calculated the band gap of h - bn about 5.97 ev . according to obtained data , are the band gap of h - bn and w - inn , respectively . is calculated to be 4.99 ev . according to these results , a type - ii band alignment forms at the w - inn / h - bn heterojunction , as shown in fig . room temperature vbm and cbm line - up of the w - inn / h - bn heterojunction , showing a type - ii band alignment we noted that lattice mismatch between w - inn ( 0001 ) and h - bn ( 0001 ) is 20% , so the critical thickness is estimated to be about 1 monolayer ( ml ) . the residual stress in the film is very small . because of the small linear pressure coefficient of inn ( ~0.06 mev / gpa ) according to his results , we estimate the magnitude of the field is in the order of 10 v / m . due to the critical thickness is about 1 ml , the band bending caused by the piezoelectric effect is about 0.06 ev . the effect of interface states is to shift the potential within the sampled region on both sides of the interface by the same constant value . and then , any potential shift which due to band bending induced by interface states can be canceled . in summary , the vbo of w - inn / h - bn heterojunction has been measured by xps to be 0.30  0.09 ev , and the corresponding cbo is 4.99  0.09 ev , so it belongs to a type - ii band line - up . based on the calculation , the effect of piezoelectric caused by the lattice mismatch and band bending by the surface state can be neglected . the accurate determination of the band alignment of w - inn / h - bn is important for designing the devices . the authors are grateful to professor huanhua wang and dr . tieying yang of the institute of high energy physics , chinese academy of science . this work was supported by national science foundation of china ( no.60776015 , 60976008 ) , the special funds for major state basic research project ( 973 program ) of china ( no.2006 cb604907 ) , and the 863 high technology r&d program of china ( no.2007aa03z402,2007aa03z451 ) . this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited . this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .