什么是III-V 族化合物半导体？

经常看到很多iii v族化合物半导体的说法，比如砷化镓、铟镓磷和氮化镓，这些元素都在周期表的三族和五族里面。这些化合物半导体有什么基本特征呢？

A III-V compound semiconductor is an alloy,containing elements from groups III and V in the periodic table.

Different material systems combining these elements have been produced, the most commonly known of which is GaAs.Within the III-V semiconductors there are the nitride semiconductors subset. At Warwick, there is extensive research into nitride semiconductors in the Surface, Interface and Thin Film Group.

GaN

GaN and its alloys offer many advantages compared to a III-As system, particularly a much wider range of energy bandgaps. Optoelectronic devices based on nitride ternary alloys can operate atenergies in the mid ultraviolet all the way to infrared. The AlGaN/GaN heterojunction has a large band discontinuity that can allow GaN devices tohave improved output power density and improved thermal conductivity means they can operate effectively at higher temperature.

Recent interest in short wavelength lightemitting diodes (LEDs) and laser diodes (LDs) has led to the development ofnitride based blue LEDs and ultraviolet LDs, with a wide range of applications.

GaN normally crystallizes in thehexagonal/wurtzite structure, which is subject to strong internal spontaneous and piezoelectric fields. These fields can reduce the efficiency of LEDs andLDs by reducing the overlap of wavefunctions in the quantum well. For thisreason, attempts have been made to grow non-polar bulk hexagonal crystals, but these produced poor results.

The GaN can instead be grown directly inthe non-polar direction in a cubic structure, which eliminates the internalfields. In addition, the material can be cleaved in perpendicular planes andthere is improved electron and hole mobility due to the symmetric structure.Growing purely cubic GaN structures is difficult due to their thermo dynamicinstability, which leads to hexagonal inclusions forming, especially in thickerlayers. Research is currently being undertaken to improve cubic GaN growth techniques. Bulk cubic GaN would be useful as a substrate for devices as strainand dislocation effects would be minimised at the interface.

Once device that also makes use of III-N materials is the Resonant Tunnelling Diode (RTD) that has many useful properties, the most notable being its Negative Differential Resistance (NDR).Efforts are being undertaken to improve the quality of these devices, indicatedby their peak to valley current ratio (PVR). An NDR made of cubic nitridematerial would benefit from more reproducible tunnelling without the internalfields of hexagonal structures.

InN

Indium nitride is a direct narrow bandgap semiconductor (~0.7 eV at room temperature), with potential in high speed optoelectronics and solar cells[1]. When combined with gallium to produce theternary alloy InGaN, the bandgap is tunable over the range 0.7 - 3.4 eV, fromthe infra-red to the ultraviolet, encompassing the entire visible spectrum, asshown in the figure below comparing the lattice constant to the room temperature bandgap of many compounds.

Bandgap vs. lattice constant for manysemiconductor compounds [4].

InN has extreme properties, particularly anextreme electron accumulation at all surfaces, in contrast to most other III-Vcompounds that exhibit an electron depletion layer. InN is a heavilyunintentionally n-type doped system, due to defects within the lattice, and theproperty of the branch point energy being well above the conduction band minimum, making the defects donor-like. As a result p-type doping is proving adifficult task, and currently research into doping the system with Mg is ongoing in different research groups[2].

InN exists in both a wurtzite, and zincblende structure, but more commonly as wurtzite. The zinc blende structure requires specific growth conditions, including the use of a zinc blendesubstrate. The atomic structure of wurtzite InN at the surface has been investigated through the use of ion scattering spectroscopy to determine thereconstruction at the surface[3]. The results of the ion scattering has led tothe proposal of a model involving three In adlayers at the surface of the thepolar InN (0001).

In tri-layer model, as published in [3].

Dilute Magnetic Semiconductors

In an effort to incorporate magnetism into existing semiconductor structures, a magnetic dopant (Cr, Mn, Fe, Ni, Co, Gd)is included into the material during growth. The exchange coupling between these dopants leads to magnetic properties.

References

T. D. Veal, C. F. McConville, and W. J.Schaff (Eds), Indium Nitride and Related Alloys (CRC Press, 2009).

R. E. Jones, et al, Physical ReviewLetters, 96, 125505, (2006).

T. D. Veal and P. D. C. King and M. Walkerand C. F. McConville and Hai Lu and W. J. Schaff, Physica B, 401-402, 351,(2007)

http://www-opto.e-technik.uni-ulm.de/lehre/cs/

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