News Article

Improving Polar InN Surfaces

Using a simple nitridation process, it is now possible to grow up to 25nm thick polar InN films with the surface Fermi level close to the valence band maximum. Substrates used include silicon (111) and GaN (0001)
A Finnish-Russian-Swedish collaboration is claiming that it has used ammonia nitridation to produce the first polar InN with the surface Fermi level near the valence-band maximum.

In the past, the growth of polar InN films has been hindered due to metallic indium clusters, formed readily during growth, and unintentional n-type conductivity of nominally undoped films. These include surface electron-accumulation layers via the Fermi level pinning into the conduction band.

These issues have hampered, for example, the realisation of p-type InN layers. This makes it difficult to grow p-n junctions in InN layers, which are needed in devices such as those used in solar, power electronic and LED applications.

A team from the Institute of Solid State Theory, Friedrich Schiller University and the European Theoretical Spectroscopy Facility, all based in Germany, using ab initio calculations, recently predicted the Fermi level position for InN [1]. Furthermore, researchers at Ritsumeikan University in Japan and Seoul National University, Korea have shown that the plasma nitridations during growth stops transform even large indium clusters into two-dimensional InN islands, improving InN quality [2].

Now researchers, led by a team at the University of Turku in Finland, have shown that high electron concentrations can be avoided, which is promising for making p-type InN films.

They initially grew InN films on silicon (111) and GaN (0001) substrates by the nitridation of the indium-covered semiconductor surfaces with ammonia (NH3) or cracked N2 gas.

Following this treatment, the scientists found it was possible to grow up to 25nm thick polar InN films with the surface Fermi level close to the valence band maximum. In other words, they avoided the presence of electron accumulation layers. The plot below shows the Fermi level obtained using Scanning Tunnelling Spectroscopy (STS).

Analysis of current-voltage curves, measured by STS from well-defined surface areas, reveal that the surface Fermi level locates close to the valence-band maximum


Synchrotron-radiation In 4d core-level photoelectron spectra show that the nitridation transform metallic indium to InN

The substrate temperature during the nitridation was found to be one of the most crucial parameters in the formation of InN (000-1) films with the Fermi level near the valence-band maximum.

Indium was evaporated from a heated tantalum envelope onto the substrates, which were kept at room temperature before nitridations. The NH3 pressure was about 5 x 10-5 mbar during the nitridation. Temperature of indium-covered silicon (111) substrates was 400 - 450 °C during the nitridation, and the temperature for indium-covered GaN (0001) pieces was 530 - 580 °C, just below the decomposition temperature of InN.

The silicon (111) substrates were flash heated at about 1200 °C. STM indicates a smooth, well-defined (7x7)-reconstructed surface.

STM image showing two-dimensional nature of InN (000)/Si (111) sample (~ 800 nm x 800 nm)

To clean HVPE-grown n-type GaN (0001) substrate pieces, they were heated to around 600 °C in the NH3 atmosphere to get a sharp (1 x 1) diffraction.

STM image showing two-dimensional nature of InN (000)/GaN (0001) sample (~450nm x 450nm)

Further details of this work have been published in the paper, "Formation of polar InN with surface  Fermi level near the valence band maximum by means of ammonia nitridation" by J. Dahl et al in Physical Review B, 86, 245304 (2012). DOI: 10.1103/PhysRevB.86.245304


[1] A. Belabbes, J. Furthmüller, and F. Bechstedt, Phys. Rev. B 84, 205304 (2011)

[2] T. Yamaguchi and Y. Nanishi, Appl. Phys. Expr. 2, 051001 (2009).

AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.



Search the news archive

To close this popup you can press escape or click the close icon.
Register - Step 1

You may choose to subscribe to the Compound Semiconductor Magazine, the Compound Semiconductor Newsletter, or both. You may also request additional information if required, before submitting your application.

Please subscribe me to:


You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in:
Live Event