Monte Carlo study of kink effect in short-channel InAlAs/InGaAs highelectron mobility transistors

Vasallo García, Beatriz, López Mateos, Javier, Collantes Pardo, Daniel, Sánchez González, Tomás

Description

Colecciones : DFA. Artículos del Departamento de Física Aplicada
Fecha de publicación : 15-sep-2003
A semiclassical 2D ensemble Monte Carlo simulator is used to perform a physicalmicroscopic analysis of the kink effect in short-channel InAlAs/InGaAs lattice-matched High Electron Mobility Transistors (HEMTs). Due to the small band gap of InGaAs, these devices are very susceptible to suffer impact ionization processes, with the subsequent hole transport in the channel,both supposedly implicated in the kink effect and easy to be implemented in a Monte Carlosimulation. The results indicate that for high enough VDS , holes, generated by impact ionization,tend to pile up in the channel under the source side of the gate due to the attracting potential caused by the surface charge at the recess and, mostly, by the gate potential. Due to this pile up of positive charge, the potential barrier controlling the current through the channel is lowered, so that the channel is further opened and ID increases, leading to the well known kink effect in the current voltage characteristics. The microscopic understanding of this phenomenon provides valuableinformation to conceive the optimum fabrication process for kink-effect-free HEMTs.En este trabajo se utiliza un simulador Monte Carlo para analizar a nivel microscópico el origen del efecto kink en transistores HEMT de InAlAs/InGaAs de canal corto. Se encuentra que el fenómeno es debido a huecos, generados por mecanismos de ionización por impacto, que se acumulan en el canal debajo de la puerta del transistor en el lado de la fuente. Tal acumulación reduce la barrera de potencial que controla la corriente que circula por el canal, de modo que ésta aumenta. Se proporcionan indicaciones de diseño para optimizar la fabricación de transistores libres de efecto kink.

Informations

• Publié par: Salamanca
• Publié le: 15 septembre 2003
• Nombre de lectures: 18
• Licence : En savoir +
  Paternité, pas d'utilisation commerciale, partage des conditions initiales à l'identique
• Langue: Español

Extrait

nloaded 30 Sep 2DwoP lio AIe orcensnos ubittct buej. 66.169ristdiRe2 ot 3001.821.21ps

I. INTRODUCTIONers in these devices is monitored by means of a semiclassical two-dimensional~2D!ensemble MC simulator in which both InAlAs/InGaAs high electron mobility transistors  impact ionization and hole recombination are included. This ~HEMTs!have proven a record of excellent performance for  approach allows one to determine the origin and magnitude low-noise high-frequency applications~in microwave and  of the kink effect in terms of internal quantities~like electron millimeter-wave frequency ranges!, and are used as active  and hole co and devices in high-speed integrated circuits. 1±3 However,they completeph n y c s e i n c t a r l ati u o n n d s erstand p i o n t g ent o i f al t p h r e o® k l i e n s! k ,s e o ff t e h ct at i a s have still some drawbacks to be eliminated, like the kink  achieved, thus providing some guidelines to be followed in effect, i.e., an anomalous increase in the drain currentI D at the  fabrication process of HEMTs in order to improve their suf®ciently high drain-to-source voltagesV DS , which leads  immunity to kink effect. to a reduction in the gain and a rise in the level of noise, thus  The article is organized as follows. In Sec. II, the physi- limiting the utility of these devices for microwave power  cal model is detailed. The main results of our simulations 4 applications. and  their discussion are provided in Sec. III. Finally, in Sec. When reducing the device dimensions to improve the  IV, we draw the most important conclusions of this work. frequency range of operation of HEMTs, very high electric ®elds appear in the gate±drain region of the device, which, jointly with the narrow band gap of InGaAs, makes this de- II. PHYSICAL MODEL vice very susceptible to impact ionization mechanisms. 1 As mentioned b e r the calc se Someworkssuggestthatimpactionizationandthesubse- ofanensembleMC e s f i o m r u , la f t o orself-con u s l is a t ti e o n n t s,wemakeu quent hole dynamics~jointly with trapping processes!canbe a2DPoissonsolverwhichincorporatesallt l h y e c p o r u o p c l e e s d se w s it a h t responsible for the kink effect. 4±10 However, kink phenom-  the origin of the kink effect. The structure under analysis is a ena are not still completely understood, specially in short- channel HEMTs. 4 100 nm T-gate recessed HEMT~Fig. 1!, and consists of a InP substrate~not simulated!, a 200 nm In 0.52 Al 0 48 As buffer fol- Thus, the use of a microscopic approach beyond the . rs standard drift-diffusion models typically employed to ana-  lowed by a 25 nm thick In 0.53 Ga 0.47 Aschannel,threelaye ed lyze this effect is highly desirable. The Monte Carlo~MC! l o a f ye I r n 0. m 52 o A d l e 0 l . e 48 d A a s s ~ a a 5 5 n n m m la s y p e a r ce d r o , p a ed 5 a 3 t 1 N 0 1 D 2 5 c 1 m 0 2 1 2 9 , cm d- 2 d 3 op and method has been proven to be a very useful tool when deal- ing with problems where the understanding of the micro-  a 10 nm Schottky layer!, and, ®nally, a 10 nm thick scopic behavior of carriers is essential. 11±14 Theaimofthis I et n e 0. r 5 s 3 f G o a r 0. e 4 l 7 e A c s tro c n a s p i l n ay th er ei ( n N v D ol 5 ve 5 d 3 m 1 a 0 t 1 e 8 ri c a m ls 2 c 3 ) a . n T be he fo p u a n r d am in - work is the development of a physical model for the kink  w le de ristics and noise effect in short-channel recessed In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As b R e e h f. av 1 i 1 o , rof hi thisd t e a v i i l c s e o f f o t r h l e o s w ta a ti p c pl c ie h d ara v c o t l e tages~in absence HEMTs. Toward this end, the microscopic transport of carri-  of impact ionization!can be found in Refs. 12 and 13, in which the agreement between the results of the simulations a! Electronic mail: [e-mail] and the experimental measurements con®rm the validity of 0021-8979/2003/94(6)/4096/6/$20.00 4096  2003 American Institute of Physics

JOURNAL OF APPLIED PHYSICS VOLUME 94, NUMBER 6 15 SEPTEMBER 2003 Monte Carlo study of kink effect in short-channel InAlAsÕInGaAs high electron mobility transistors B. G. Vasallo, a) J.Mateos,D.Pardo,andT.Gonza  lez DepartamentodeFõ  sicaAplicada,UniversidaddeSalamanca,PlazadelaMerceds/n, 37008 Salamanca, Spain ~Received 12 February 2003; accepted 25 June 2003! A semiclassical two-dimensional ensemble Monte Carlo simulator is used to perform a physical microscopic analysis of the kink effect in short-channel InAlAs/InGaAs lattice-matched high electron mobility transistors~HEMTs!. Due to the small band gap of InGaAs, these devices are very susceptible to suffer impact ionization processes, with the subsequent hole transport in the channel, both supposedly implicated in the kink effect and easy to be implemented in a Monte Carlo simulation. The results indicate that for high enoughV DS , holes, generated by impact ionization, tend to pile up in the channel under the source side of the gate due to the attracting potential caused by the surface charge at the recess and, mostly, by the gate potential. Due to this pile up of positive charge, the potential barrier controlling the current through the channel is lowered, so that the channel is further opened andI D increases, leading to the well known kink effect in the current± voltage characteristics. The microscopic understanding of this phenomenon provides valuable information to conceive the optimum fabrication process for kink-effect-free HEMTs. 2003 American Institute of Physics.@DOI: 10.1063/1.1603955#

/japcr.jorg/japo.spj.piapttho//:, hte seop cigyr