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.
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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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    ABSTRACT: An auto-split laser lift-off (LLO) method for fabrication of vertical-injection GaN-based green light-emitting diodes (ASV-LEDs) is demonstrated. The ASV-LEDs exhibited a significant improvement in the light output and thermal dissipation, as compared with that of conventional LEDs on sapphire. The intrinsic physical mechanism of the auto-split LLO technique is studied by a Frank-Read dislocation clustering model. The laser energy density and mesa spacing are shown to be key factors in the auto-split LLO method. It is believed that this method offers an alternative way to fabricate high-performance GaN-based thin-film LEDs.
    Preview · Article · Aug 2013 · IEEE Photonics Journal
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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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