Black diamond has been demonstrated as a material capable o f both high carrier concentrations and mobilities, com parable with that o f the best single crystal diamond. It is very surprising that this is possible in such a highly defective material. It has been suggested that this may be due to the application of the hydrogen surface conductivity layer, as this is situated in the near surface of the diamond. As this conductivity is also activated by a hydrogen plasma, the possibility of the surface being etched of contaminants has also been raised.
If it is possible to passivate the surface conductivity layer to remove such atmospheric effects as detailed in chapter seven, then black diamond could be seen as a cheap and effective alternative to white / single crystal material.
C h a p te r 8: H y d r o g e n a te d B la ck D ia m o n d
References
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Ristein J., M aier F., Riedel M., Stammer M. and Ley L., Diamond and Related Materials 10 (2001) 416
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C h a p te r 9: P o lis h e d P o ly o y s ta llin e C V D D ia m o n d
Chapter 9
Polished Polycrystalline CVD Diamond
C o n te n ts
Section 9.1
Introduction
Section 9.2
Experimental Aims
Section 9.3
Experimental Methods
Section 9.4
Section 9.4.1 S ection 9.4.2 Section 9.4.3Experimental Results
Raman Hall Data Device C h aracteristicsSection 9.5
Discussion
Section 9.6
Summary
C h a p te r 9: P o lish e d P o ly e ry sta llin e C V D D ia m o n d
Section 9.1 Introduction
If the “A chilles H eel” o f diamond is the resulting polyerystalline nature of hétéroépitaxial diamond films, then polishing could be a promising solution. Flat films are vital for the utilisation of photolithography during device fabrication and hence the only valid substrate for micron and smaller scale devices.
However polishing diamond is something of a “black art” and little is known about the possible negative effects on device characteristics due to surface damage. Conventional mechanical polishing is performed using diamond powder of various grain sizes, starting with a large grit for high speed, and reducing to finer powder for a smoother surface [Malshe 1999]. However, there is a limit on the minimum roughness achieved by this technique due to micro cavities formed by the polyerystalline growth m echanism of diamond. These micro cavities appear as pits on the surface as the diam ond is polished, and a planarisation technique must be used to fill in these surface pits [Malshe 1994].
As with previous work, this chapter utilises the hydrogen surface conductivity layer and hence plasma exposure could etch damage effects from the surface.
Section 9.2 Experimental Aims
The aim o f work outlined in this chapter is to assess the use o f polished polyerystalline diam ond for device applications using the hydrogen surface conductivity layer.
Section 9.3 Experimental Methods
The diam ond used in this chapter was a comm ercially available polished white polyerystalline diamond. RAMAN spectra were taken with a RENISHAW 2000 system with red (He-Ne) laser excitation.. Prior-to hydrogenation all samples were im m ersed in a boiling ammonium persulphate / sulphuric acid mixture which is known to result in a contaminant free oxidised surface [Baral 1996]. Hydrogenation was perform ed using pure atomic hydrogen plasma generated within a purpose built
C h a p te r 9: P o lish e d P o lyery sta llin e C VD D iam on d
M W PECVD chamber (sample temperature 500"C, 800W, 40torr, 5 minutes). Au contacts were thermally evaporated in the Van Der Pauw configuration for conformai mapping using an Edwards A306 evaporator with a base pressure better than 4x10'^ mbar. Hall effect measurements were carried out in a vacuum better than 6x10'^ mbar (10-300K, 0.3-1.8 T magnetic field strength). A1 was deposited with an Edwards A306 evaporator with a base pressure better than 4x10^ m bar to a thickness of 300nm. The structure of the schottky conacts were defined with photolithography as a
200pm dot using etching. The lift off technique was used to define the Au ohmic. I / V Testing was perform ed with a H ew lett Packard HP4145B Sem iconductor Parameter Analyser.