Favourable growth conditions for the preparation of bulk AlN single crystals by PVT

Abstract

A high seed temperature (2251 °C) reveals the highest deep UV transparency (α265nm = 27 cm−1), a high structural perfection (EPD = 9 × 103 cm−2) and a suitable growth rate (R = 200 μm h−1).

Photochromism and influence of point defect charge states on optical absorption in aluminum nitride (AlN)

“…The measurement of the m-cut sample for E⊥c polarization corresponds to measurements of c-plane AlN wafers reported previously. 6,15,49,50 Several unresolved absorption bands in the range below 4.0 eV are observed for areas B1 and B3, while in area B2 no absorption bands are found (α<5 cm -1 ), so area B2 appears colorless to the eye. The band peaking at 4.7 eV, usually referred to as "carbon related", was observed in areas B1 and B2; this was discussed previous studies also from our group.…”

“…The band has been earlier reported to be polarization-dependent in oxygen-dominated samples and its intensity correlates with high oxygen concentrations. 6,26,67,68 From the absorption peak energy and the temperature of the thermally-induced restoration, the position below CB is estimated to be 1.0 -2.5 eV and 1.0 -1.2 eV, respectively. Thus, both thermal and optical activation of the state can be associated with the same defect level, only if this value is roughly close to 1 eV.…”

“…Suitable AlN bulk crystals are typically grown by physical vapor transport (PVT). [5][6][7] Optical and electrical properties of the material are determined by intrinsic defects, such as aluminum and nitrogen vacancies (V Al , [8][9][10][11][12][13][14] V N 15,16 ), and extrinsic defects from unintentional background doping by silicon, oxygen, and carbon. These three impurities provide not only isolated substitutional defects (i.e., oxygen and carbon substituting nitrogen, and silicon substituting aluminum: O N, C N, Si Al ), [17][18][19][20][21][22] but are also assumed to form complexes, such as V Al -nSi Al , 23 V Al -nO N (n=1…4 is a number of Si or O atoms), 13,14,16,[23][24][25][26][27][28] C N -Si Al , 29 carbon pairs, 30 and tri-carbon complexes.…”

Realizing overgrowth in the homo-PVT process for 2 inch AlN single crystals

“…Some groups have developed 2 inch crack-free [6][7][8][9] or ponysized high quality 10,11 AlN single crystals, but these products are mostly prepared for private use in limited quantities instead of industrialization, which indicates the existence of serious problems in the manufacturing of PVT-AlN crystals. Two technical routes are commonly applied to the PVT growth of AlN, which are spontaneous nucleation 12 with subsequent enlargement 13 or large-size heterogeneous growth on SiC followed by several generations of homogeneous growth optimization on AlN. 7 The former route is good for high crystal quality but difficult for enlargement efficiency and the barrier for mass production is extremely high.…”

X-ray characterization of physical-vapor-transport-grown bulk AlN single crystals

“…While a slow but steady increase of wafer diameters can be achieved by repeated PVT bulk growth (Hartmann, 2013;Raghothamachar et al, 2012), limited data are available about the development of crystallographic defects along the axial ([0001] or [0001]) and lateral growth directions during diameter enlargement and the underlying mechanisms for defect formation. It has been pointed out (Hartmann et al, 2020) that a careful design of axial and radial temperature gradients in the growth zone is necessary to reduce the density of grown-in dislocations. As a consequence, typically employed expansion angles (Dalmau et al, 2018) allow only for a moderate diameter expansion within a single growth run to avoid degradation of the crystal quality.…”