Hardness and Fracture Toughness of Bulk Single Crystal Gallium Nitride

Lawrence Berkeley Laboratory, University of California, Berkeley, Berkeley, California, United States
Applied Physics Letters (Impact Factor: 3.3). 01/1997; 69(26):4044 - 4046. DOI: 10.1063/1.117865
Source: IEEE Xplore


Basic mechanical properties of single crystal gallium nitride are measured. A Vickers (diamond) indentation method was used to determine the hardness and fracture toughness under an applied load of 2N. The average hardness was measured as 12±2 GPa and the average fracture toughness was measured as 0.79±0.10 MPa√m. These values are consistent with the properties of brittle ceramic materials and about twice the values for GaAs. A methodology for examining fracture problems in GaN is discussed. © 1996 American Institute of Physics.

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    • "Most of the work in this direction is carried on polycrystalline [4], ceramics [5] and metals [6] but few reports are also available on single crystals [7] [8] [9] [10]. Fang and Lambropoulos [11] have made a systematic study on fracture toughness of KDP crystals, surprisingly similar studies on fracture toughness are lacking on ADP crystals, which is a second harmonic generation (SHG) material. "
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    ABSTRACT: tIn the present work, Vickers microhardness measurements were carried out on different faces i.e. (1 0 0),(0 0 1) and (1 0 1) of ammonium dihydrogen phosphate (ADP) single crystals grown by slow evaporationsolution technique at room temperature in the load ranging from 0.2 to 2 N. The obtained results showthat the load independent hardness values are 0.8, 0.7 and 0.66 GPa, respectively at different faces ofADP crystal. From the crack length measurements, the fracture toughness values (Kc) was estimatedusing Evans and Anstis model and the present studies suggest that Evans model is more relevant whencompared to Anstis model. The load variation of some mechanical properties viz. brittle index number(Bi) and yield strength (�y) for ADP have also been calculated for the first time.
    Optik - International Journal for Light and Electron Optics 07/2014; 125(13):3268–3271. DOI:10.1016/j.ijleo.2013.12.046 · 0.68 Impact Factor
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    • "There is a common feature in the observed fracture of the freestanding films shown in Fig. 2 and in our previous work [30]. It is that the cracking pattern is very similar to Bceramic fragmentation[, indicating that the properties of GaN film are consistent with that of brittle ceramic materials [32]. Such a pattern of cracks is the so-called brittle fracture. "
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    IEEE Photonics Journal 08/2013; 5(4):8400407-8400407. DOI:10.1109/JPHOT.2013.2274768 · 2.21 Impact Factor
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    • "Figure 2. is the macro sketch of this method, we attach our sample on a copper column then put it on a rotational platen. As we know the surface microhardness of GaN is between 1200-1700 kg mm -2 which is more harder than 790 kg mm -2 of SiO 2 [4] [5], so we can remove SiO 2 layer without damaging GaN by controling the force properly on the copper column. We use Al 2 O 3 particles slurry to perform the mechanical polishing process which is shown in figure 2. The particles size of Al 2 O 3 is about 800nm. "
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