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¹²ÕñËí´©¾§Ìå¹Ü English Abstract First-principles study of graphyne/graphene heterostructure resonant tunneling nano-transistors Wang Tian-Hui 1 ,Li Ang 1 ,Han Bai 2 1.School of Disciplinary Basics and Applied Statistics, Zhuhai College of Jilin University, Zhuhai 519041, China 2.Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Heilongjiang Provincial Key Laboratory of Dielectric Engineering, School of Electrical and Electronic Engineering, Harbin University of Science and Technology, Harbin 150080, China Fund Project: Projects supported by the National Natural Science Foundation of China (Grant No. 51607048) and the Young Innovative Talent Training Program of Heilongjiang Province Undergraduate Colleges and Universities, China (Grant No. UNPYSCT-2016049). Received Date: 01 June 2019Accepted Date: 10 July 2019Available Online: 01 September 2019Published Online: 20 September 2019 Abstract: Resonant tunneling transistors have received wide attention because of their ability to reduce the complexity of circuits, and promise to be an efficient candidate in ultra-high speed and ultra-high frequency applications. The chemical compatibility between graphene and graphdiyne implies that they can be combined into various configurations to fulfill ultra-high frequency nanotransistor. In the present paper, two novel resonant tunneling transistors based on graphene/graphdiyne/graphene double-heterojunction are theoretically developed to model two new kinds of bipolar devices with two representative graphdiyne nanoribbons. The electronic structures of two pristine graphdiyne nanoribbons are investigated by performing the first-principles calculations with all-electron relativistic numerical-orbit scheme as implemented in Dmol3 code. The electronic transport properties including quantum conductance (transmission spectrum) and electrical current varying with bias-voltage for each of the designed graphdiyne nanoribbon transistors are calculated in combination with non-equilibrium Green function formalism. The calculated electronic transmission and current-voltage characteristics of these transistors demonstrate that the current is dominantly determined by resonant tunneling transition and can be effectively controlled by gate electric field thereby representing the favorable negative-differential-conductivity, which is the qualified attribute of ultra-high frequency nanotransistor. It follows from the I -U b variations explained by electronic transmission spectra that quantum resonance tunneling can occur in the proposed star-like graphdiyne (SGDY) and net-like graphdiyne (NGDY) nanoribbon transistors, with the resonance condition limited to a narrow bias-voltage range, leading to a characteristic resonant peak in I -U b curve, which means the strong negative differential conductivity. Under a gate voltage of 4 V, when the bias-voltage rises up to 0.6 V (0.7 V), the Fermi level of source electrode aligns identically to the quantized level of SGDY (NGDY) nanoribbon channel, causing electron resonance tunneling as illustrated by the considerable transmission peak in bias window; once the source Fermi level deviates from the quantized level of SGDY (NGDY) channels at higher bias-voltage, the resonance tunneling transforms into ordinary electron tunneling, which results in the disappearing of the substantial transmission peak in bias window and the rapid declining of current. The designed SGDY and NGDY nanotransistors will achieve high-level negative differential conductivity with the peak-to-valley current ratio approaching to 4.5 and 6.0 respectively, which can be expected to be applied to quantum transmission nanoelectronic devices. 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Èç¹ûûÓÐÍⲿƫÖÃ, µç×ÓµÄÊäÔËÌØÐÔ¿ÉÓɹ«Ê½(1 )ºÍ(2 )ÃèÊö; µ±Íⲿƫѹ×÷ÓÃÔڵ缫ÉÏʱ, Ö»»áÒýÆðÌØÕ÷ÖµµÄ¸ÕÐÔÆ«ÒÆ. һάϵͳÖеç×ӵ絼¿ÉÒÔ¿´×÷ÊÇÒ»¸ö´«µÝÎÊÌâ, µçÁ÷ÓɸñÁÖº¯Êýͨ¹ýLandauer Buttiker¹«Ê½µÃµ½[28 ] : ÆäÖÐf L (E ,V )ºÍf R (E ,V )·Ö±ð±íʾƫѹV ×÷ÓÃÏÂ×óÓÒÁ½¶Ëµç¼«µÄ·ÑÃ×-µÒÀ¿ËÄÜÁ¿·Ö²¼º¯Êý.3.½á¹ûÓëÌÖÂÛ Ê×ÏȶÔÁ½ÖÖµäÐ͵ÄʯīϩÄÉÃ×´ø¡ªÐÇÐÎʯīȲ(SGDY)ºÍÍø״ʯīȲ(NGDY)ÄÉÃ×´ø½øÐеÚÒ»ÔÀíÄÜÁ¿·ºº¯¼¸ºÎÓÅ»¯ºÍµç×ӽṹ¼ÆËã, ÔÙ¹¹½¨Ë«¼«Æ÷¼þ(Èçͼ1 Ëùʾ)ÓÃÒÔ¼ÆËãÁ¿×ÓÊäÔËÌØÐÔ. ÓÉÓÚʯīȲ/ʯīϩ½çÃæ´æÔÚ¾§¸ñʧÅä, Òò´Ë¼¸ºÎÓÅ»¯ÒÔºóÔÚʯīȲ/ʯīϩÒìÖʽáÄÉÃ×´ø½çÃæ´¦µÄʯīȲ̼Ô×Ó»·ÏòÄÉÃ×´øÖÐÐÄƫת±äÐÎ, ÒìÖʽá½çÃæ´¦µÄʯīȲºÍʯīϩÄÉÃ×´ø·Ö±ð²úÉúѹӦ±äºÍÀÉìÓ¦±ä. ÓÉÓÚ¸ÃÓ¦±äÖ÷ÒªÊÇ̼Ô×ÓÖ®¼äµÄ³É¼ü½Ç¶È·¢ÉúÇá΢µÄ±ä»¯, ËùÒÔÓ¦±ä²úÉúµÄÓ¦Á¦ºÜС, ÒìÖʽṹ½ÏΪÎȶ¨. ÔÚ¹¹½¨µÄË«¼«Æ÷¼þÖÐ, SGDYºÍNGDYÄÉÃ×´ø¹µµÀµÄ³ß´ç(³¤ ¡Á ¿í)·Ö±ðΪ(28.6 ? ¡Á 8.9 ?)ºÍ(34.2 ? ¡Á 16.1 ?). ²ÉÓûùÓÚÈ«µç×ÓÊýÖµ¹ìµÀ»ù×é·½·¨µÄDmol3³ÌÐò½øÐеç×ӽṹ¼ÆËã, µÃµ½SGDYºÍNGDYÄÉÃ×´øµÄµç×ÓÄÜ´ø½á¹¹Èçͼ2 Ëùʾ(ÒÔ·ÑÃ×Äܼ¶ÉèΪÄÜÁ¿²Î¿¼µã). Á½ÖÖ½á¹û¾ùδ³ÊÏÖµç×ÓÄÜÁ¿µÄ×ÔÐý·ÖÁÑ, SGDYÄÉÃ×´øµÄÄÜ´ø´ø϶Ϊ1.63 eV, ÔÚ²¼ÀïÔ¨ÇøG µã³ÊÏÖ°ëµ¼ÌåÖ±½Ó´ø϶; ¶øNGDYÄÉÃ×´ø²»´æÔÚÄÜ´ø´ø϶, ³ÊÏÖ½ðÊôÄÜ´øÌØÕ÷. ͼ 2 SGDY (a)ºÍNGDY (b)ÄÉÃ×´øµÄµç×ÓÄÜ´ø½á¹¹, ÒÔ·ÑÃ×Äܼ¶(ˮƽÐéÏß)ΪÄÜÁ¿²Î¿¼Áãµã Figure2. Electronic energy band structure of SGDY (a) and NGDY (b) nanoribbons with Fermi energy level as reference energy zero (horizontal dashed line). ΪÁËÑо¿Ëù¹¹½¨¾§Ìå¹ÜµÄµçÊäÔËÌØÐÔ, ²ÉÓÃ˫̽Õë·½·¨¹¹½¨Ë«¼«Æ÷¼þ, ½«Ê¯Ä«È²ÄÉÃ×´ø×÷ΪÖÐÐÄÉ¢ÉäÇøÓòÓëÁ½¶ËʯīϩÄÉÃ×´ø°ëÎÞÏ޵缫ÏàÁ¬, ÓÃÓÚÊ©¼ÓÆ«Öõçѹ, ²¢ÔÚÄÉÃ×´øƽÃæ´¹Ö±·½Ïò¹¹½¨ÓÃÓÚÊ©¼ÓÕ¤¼«U g µÄÕ¤µç¼«(Èçͼ3 Ëùʾ), ¼ÆË㲻ͬU g ϵĵç×Ó͸ÉäÆ׺͵çÁ÷-Æ«Öõçѹ(I -U b )ÇúÏß. ͼ4(a) ΪSGDYºÍNGDYÄÉÃ×´øÔÚ0¡ª2 VÆ«Öõçѹ·¶Î§ÄÚµÄI -V ÌØÐÔÇúÏß(Õ¤¼«µçѹΪÁã). Ê©¼ÓU b ÔÚ1.5 V(ãÐÖµµçѹ)ÒÔÏÂ, µçÁ÷¼¸ºõΪÁã; µ±U b ³¬¹ýãÐÖµµçѹÒÔºó, Ô´¼«·ÑÃ×Äܼ¶Éý¸ßÖÁÓëʯīȲÄÉÃ×´ø¹µµÀÇøµÄÁ¿×Ó»¯Äܼ¶Ïàͬ, Ðγɵç×Ó¹²ÕñËí´©, µçÁ÷ÒÔÖ¸ÊýÐÎʽѸËÙÔö´ó. ËäÈ»SGDYÄÉÃ×´øµÄµç×ÓÄÜ´ø´æÔÚ´ø϶, µ«Æä¿í¶È½ÏС, µç×ÓÔÚÖÐÐÄÇøÊäÔ˹ý³ÌÈÔÈ»»á·¢Éú½ÏСµÄÉ¢Éä, Òò´ËSGDYÄÉÃ×´øµÄµçÁ÷ÂÔ´óÓÚNGDYÄÉÃ×´øµÄµçÁ÷. ÔÚÕ¤¼«µçѹU g = 4 Vʱ, SGDYºÍNGDYÄÉÃ×´ø¾§Ìå¹ÜµÄ©¼«µçÁ÷ËæÆ«ÖõçѹµÄ±ä»¯Èçͼ4(b) Ëùʾ. ÓÉÓÚÁ½¸öʯīϩµç¼«Ö®¼äÔØÁ÷×ӵĹ²ÕñËí´©, ÔÚU b = 0.7 V´¦³öÏÖÒ»¸öÇ¿·å, Ëæºó³öÏÖÒ»¸ö¸ºÎ¢·Öµçµ¼Çø(NDC). µ±Ê©¼ÓµÄÆ«Öõçѹ×ãÒÔʹÖÐÐÄÉ¢ÉäÇøʯīȲÁ¿×ÓÚåÄÚδռ¾ÝÁ¿×Ó̬µÄÄÜÁ¿½µµÍÖÁʯīϩԴ¼«µ¼´øÄÜÁ¿·¶Î§Ê±, Á¿×ÓÚå´¦ÓÚгÕñ̬, ËùÒÔµç×Ó¿ÉÒÔ´©¹ýʯīȲ¹µµÀÊäÔËÖÁʯīϩNGDYÄÉÃ×¾§Ìå¹ÜµÄ©¼«, ·ñÔòµçÁ÷¼¸ºõΪÁã, ¼´ÄÉÃ×¾§Ìå¹Ü¾ÍʧȥÁ˹²ÕñЧӦ. ͼ 3 ÔÚSGDY/ʯīϩÒìÖʽáÄÉÃ×´øË«¼«Æ÷¼þµÄ´¹Ö±·½ÏòÊ©¼ÓÕ¤¼«µçѹ¹¹½¨µÄ¾§Ìå¹Üµç×ÓÊäÔ˼ÆËãÄ£ÐÍ, ·ÛÉ«ÇøÓò±íʾµç¼«, »ÒÉ«¡¢°×É«¡¢ºìÉ«¡¢»ÆÉ«ºÍ·ÛɫСÇò·Ö±ð´ú±í̼¡¢Çâ¡¢Ñõ¡¢¹èºÍÂÁÔ×Ó Figure3. Electron transport calculation in transistor model of bipolar devices with the SGDY/graphene nanoribbons heterostructure as the center scattering region and semi-infinite electrodes (source and drain) respectively under the gate voltage in vertical direction. The pink areas indicate electrodes, and the gray, white, red, yellow and pink spheres represent carbon, hydrogen, oxygen, silicon and aluminium atoms respectively. ͼ 4 SGDYºÍNGDYÄÉÃ×´ø¾§Ìå¹ÜµÄ©¼«µçÁ÷ËæÆ«ÖõçѹµÄ±ä»¯¡¡(a) U g = 0 V; (b) U g = 4 V Figure4. Drain current of SGDY and NGDY nanoribbon transistors varying with bias voltage under (a) U g = 0 V and (b) U g = 4 V µ±Æ«ÖúÍÕ¤¼«µçѹΪÁãʱ, Á½¸öʯīϩµç¼«µÄ»¯Ñ§ÊÆλÓÚµÒÀ¿Ëµã, ¾ßÓÐÏàͬµÄÄÜÁ¿. ͨ¹ýÔö¼ÓÆ«Öõçѹ, µç×ӺͿÕѨ·Ö±ðÔÚ¸º¼«ºÍÕý¼«ÖлýÀÛ, ´Ó¶ø²úÉúµç³¡, ʹµÒÀ¿Ëµã´íλ. Èç¹ûU g ¡Ù 0, ¿ÉÒÔµ÷½ÚU b ʹÁ½¸öµç¼«µÄµÒÀ¿Ëµã¶ÔÆë. Òò´ËÔÚÁ½¸öµç¼«»¯Ñ§ÊÆÖ®¼äÄÜÁ¿Çø¼äµÄÈ«²¿ÔØÁ÷×ÓÔÚI -V ÇúÏßÉÏÐγÉÒ»¸öÇ¿·å. Õ¤¼«µçѹU g = 4 Vʱ, SGDY¾§Ìå¹ÜÔÚÆ«Öõçѹ0¡ª1.0 V·¶Î§Äڵĵç×Ó͸ÉäÆ×Èçͼ5 Ëùʾ. ½«Æ«Öõçѹ´Ó0Ôö¼Óµ½0.6 V, Ô´¼«·ÑÃ×Äܼ¶ÓëʯīȲÄÉÃ×´ø¹µµÀµÄÁ¿×Ó»¯Äܼ¶Ïàͬ, Ðγɵç×Ó¹²ÕñËí´©, ÔÚÆ«Öô°¿Ú(¨CeV/2, +eV/2)³öÏÖÃ÷ÏԵĵç×ÓÊäÔË·å(Èçͼ5 ÖÐÁ½Ìõ´¹Ö±ÐéÏßËùʾÇøÓò), Òò´ËÓÉÆ«Öô°¿ÚÖÐ͸É亯Êý»ý·ÖÈ·¶¨µÄµçÁ÷Ò²ËæÖ®Ôö´ó. ½«Æ«Öõçѹ´Ó0.6 VÔö¼Óµ½0.65 Vʱ, Ô´¼«·ÑÃ×Äܼ¶ÓëʯīȲÄÉÃ×´øµÄÁ¿×Ó»¯Äܼ¶·¢ÉúÆ«Àë, ¹²ÕñËí´©×ª±äΪÆÕͨµÄµç×ÓËí´©, µ¼ÖÂÆ«Öô°¿ÚÄڵĵç×Ó͸ÉäÆ×·åÏûʧ, Òò´ËµçÁ÷ͻȻ¼õС, ±íÏÖΪÃ÷ÏÔµÄNDC, ʹSGDY¾§Ìå¹ÜµÄPVR´ïµ½ÁË4.5. PVRÊÇÖ¸¹²ÕñËí´©¹ý³ÌÖеçÁ÷×î´óÖµÓë×îСֵµÄ±ÈÖµ, PVRÔ½¸ßµç×ÓÊÙÃüÒ²Ô½³¤, ¶øÇÒ¿ÉÒÔͨ¹ýµç×ÓÊÙÃüÉ趨Êʵ±µÄ¹¤×÷ƵÂÊ. Ïà±ÈÖ®ÏÂ, NGDY¾§Ìå¹ÜÔÚÆ«Öõçѹ³¬¹ý0.7 VÒÔºó³ÊÏÖ³ö¸üÏÔÖøµÄNDC, PVR´ïµ½ÁË6.0. ͨ¹ýÓë×î½üÎÄÏ×±¨µÀµÄ²»Í¬²ÄÁÏÄÉÃ×´ø¾§Ìå¹ÜPVR½øÐбȽÏ(Èç±í2 ËùÁÐ), ±íÃ÷SGDYºÍNGDYÄÉÃ×´øµÄPVRÖµÓÅÓÚµª»¯Åð(BN)ºÍµª»¯ïØ(GaN), Òò´Ë¿É×÷Ϊ¹²ÕñËí´©¾§Ìå¹ÜµÄÄÉÃ×¹µµÀ. ͼ 5 SGDYÄÉÃ×´ø¾§Ìå¹ÜÔÚÆ«Öõçѹ0¡ª1.0 V·¶Î§Äڵĵç×Ó͸ÉäÆ×(Õ¤¼«µçѹU g = 4 V) Figure5. Electron transmission spectra of SGDY nanoribbon transistors in the bias voltage range of 0?1.0 V under gate voltage U g = 4 V. ÄÉÃ×´øÉ¢ÉäÇø µç¼« Ñо¿·½·¨ Õ¤¼«µçѹ /V PVR Êý¾ÝÀ´Ô´ SGDY, NGDY ʯīϩ µÚÒ»ÔÀí¼ÆËã 5 4.5, 6.0 ±¾ÎÄ BN ʯīϩ ÀíÂÛ¼ÆËãºÍʵÑé 0, 20 1¡ª4 Ref. [16 ] BN ʯīϩ ÀíÂÛ¼ÆËãºÍʵÑé ¨C40, 0, 40 ¡ª Ref. [17 ] GaN-Al-GaN GaN ÀíÂÛ¼ÆËã(Matlab) ¨C1, ¨C2, ¨C3 2.66 Ref. [19 ]
±í2 ²»Í¬ÄÉÃ×´ø¾§Ìå¹ÜÔÚ²»Í¬Õ¤¼«µçѹϵÄPVRTable2. PVR for nanoribbon transistors fabricated with different materials under different gate voltage. ÀàËƵÄÁ×»¯Åð(BP)/̼»¯¹è(SiC)ÄÉÃ×´øË«ÒìÖʽṲÕñËí´©¾§Ìå¹ÜµÄ¹µµÀ(BPÄÉÃ×´ø)³¤¶ÈÖ±½ÓÓ°Ïì¹²ÕñËí´©Ìõ¼þ¼°NDCÌØÐÔ, ¹µµÀ³¤¶È¼õСʹ¹²ÕñËí´©µçÁ÷·åÖµÏÔÖøÔö¸ß, µ«NDCµÄPVR»ù±¾²»·¢Éú±ä»¯[29 ] . ͼ2 ¸ø³öµÄÄÜ´ø½á¹¹±íÃ÷SGDYÄÉÃ×´øµÄµ¼´øµ×µç×ÓÓÐЧÖÊÁ¿Ã÷ÏÔСÓÚNGDY·ÑÃ×Äܼ¶¸½½üµÄµç×ÓÓÐЧÖÊÁ¿. ÓÉ´Ë¿ÉÒÔÅжÏ: SGDYÄÉÃ×´ø¹²ÕñËí´©¾§Ìå¹ÜµÄµç×ÓÉ¢ÉäÖ÷Òª·¢ÉúÔÚÔ´¼«»ò©¼«(ʯīϩÄÉÃ×´ø)Óë¹µµÀ(ÖÐÐÄÉ¢ÉäÇøµÄʯīȲÄÉÃ×´ø)µÄÒìÖʽá½çÃ渽½ü(Ëí´©ÊÆÀÝÇø), ËùÒÔ¹µµÀ³¤¶È¶ÔÆ÷¼þ·¢Éú¹²ÕñËí´©Ê±µÄI -U b ÇúÏßÌØÕ÷Ó°ÏìºÜС; ¶øµç×ÓÔÚNGDYÄÉÃ×´ø¹²ÕñËí´©¾§Ìå¹ÜµÄ¹µµÀÖÐÒ²»á·¢ÉúÃ÷ÏÔµÄÉ¢Éä, ËùÒÔ¼õСNGDYÄÉÃ×´ø³¤¶È½«µ¼Ö¹²ÕñËí´©µçÁ÷Ã÷ÏÔÔö´ó. ´ËÍâ, ÓÉÓÚË«ÒìÖʽáÆ÷¼þÖмäʯīȲÄÉÃ×´øµÄÁ¿×Ó»¯Äܼ¶ËæÆ䳤¶ÈµÄÔö¼Ó¶øϽµ, ËùÒÔ²úÉú¹²ÕñËí´©ËùÐèÒªµÄÕ¤¼«µçѹ½«Ëæ¹²ÕñËí´©¾§Ìå¹Ü¹µµÀ³¤¶ÈµÄÔö¼Ó¶ø½µµÍ.4.½á¡¡ÂÛ ¹²ÕñËí´©¾§Ìå¹ÜÒòÆä½µµÍµç·¸´ÔÓÐÔµÄÄÜÁ¦¶øÊܵ½¹ã·º¹Ø×¢, ÔÚ³¬¸ßËٺͳ¬¸ßƵӦÓÃÁìÓòÊÇÒ»¸ö·Ç³£ÓÐǰ;µÄºòÑ¡Æ÷¼þ. ±¾ÎÄͨ¹ýÀíÂÛ¼ÆËãÖ¤Ã÷: SGDYºÍNGDYÄÉÃ×´ø¾§Ìå¹ÜÖпÉÒÔ·¢Éú¹²ÕñËí´©Á¿×ÓЧӦ; ¹²ÕñÌõ¼þ¾ÖÏÞÔÚÏÁÕÆ«Öõçѹ·¶Î§ÄÚ, ʹI -U b ÌØÐÔ³öÏÖгÕñ·å, ´Ó¶ø²úÉúÇ¿¸ºÎ¢·Öµçµ¼. SGDYºÍNGDYÄÉÃ×¾§Ìå¹Ü¾ßÓиºÎ¢·Öµçµ¼ºÍ¸ß·å¹ÈµçÁ÷±È(PVRΪ4.5ºÍ6.0), ¿ÉÓÐЧµÄÓ¦ÓÃÓÚÁ¿×Ó´«ÊäÄÉÃ×µç×ÓÆ÷¼þ.