SURFACE CLEANING, ELECTRONIC STATES AND ELECTRON-AFFINITY OF DIAMOND(100), DIAMOND(111) AND DIAMOND(110) SURFACES

The effects of cleaning natural type IIb diamond (100), (111) and (110 ) samples by annealing and hydrogen - or deuterium plasma exposure wer e investigated by means of ultraviolet photoemission spectroscopy (UPS ). Different wet chemical cleaning processes (a conventional chromic a cid clean and an electrochemical etch) and a H plasma exposure have be en employed to clean natural type IIb semiconducting diamond C(100) wa fers. The effects of these processes on the diamond surface have been assessed and compared. As evidenced by Auger electron spectroscopy (AE S), an oxygen free surface could be obtained following vacuum annealin g to 900 degrees C for the electrochemical process compared to 1050 de grees C for the chromic acid etch. In addition, the technique of atomi c force microscopy demonstrated the presence of oriented pits on the s urface of samples that were electrochemically etched for long times at high currents. After a H plasma exposure the negative electron affini ty (NEA) peak in the UPS spectra doubled in intensity. An anneal to 11 00 degrees C resulted in the removal of the sharp NEA feature. A secon d H plasma treatment resulted in the reappearance of the NEA peak simi lar to that after the first H plasma exposure. A (2 x 1) reconstructed low energy electron diffraction pattern was observed subsequent to th e anneals as well as the Ii plasma treatments. The fact that a NEA can be induced or removed repeatedly by means of a H plasma exposure or a nnealing at 1100 degrees C, respectively, provides evidence to correla te the appearance of a NEA with the presence of a monohydride terminat ed surface. Corresponding effects were found for (111) and (110) surfa ces. A NEA could be induced by a H plasma and removed by annealing at 900 or 800 degrees C for diamond(111) or(110) surfaces, respectively. Following a deuterium plasma exposure the diamond surfaces exhibited a NEA like the ones treated by a hydrogen plasma. Higher annealing temp eratures were necessary to remove the NEA for deuterium due to the iso tope effect. Values of 79 and 81 V mu m(-1) were measured for the fiel d emission threshold of the oxygen terminated C(100) and C(110) surfac es, respectively. A value of 25 V mu m(-1) was determined for the hydr ogen terminated C(110) surface. (C) 1998 Elsevier Science B.V. All rig hts reserved.