Reducing dislocations of Al-rich AlGaN by combining AlN buffer and AlN/Al0.8Ga0.2N superlattices

Subquantum-Well Influence on Carrier Dynamics in High Efficiency DUV Dislocation-Free AlGaN/AlGaN-Based Multiple Quantum Wells

“…The thicknesses of the various pre-MQW layers indicated in the STEM image are typical of similar structures grown on sapphire. 21,22 As expected, no TD defects are observed, as confirmed in the HR-STEM plan-view images of the structure shown in Figure 1b, where no evidence of spots that are characteristic of TD defects is found. 23−25 This is not surprising, considering that the MQWs are preceded by an AlN buffer layer that was homoepitaxially grown on an AlN substrate characterized by very low TD density (typically <10 4 cm −2 ).…”

“…26 In addition, the SLS structure further mitigates the propagation of TDs to subsequent layers. 17,22,27 A magnified image of the MQWs and EBL layers is shown in Figure 2a, further confirming that the MQWs are well-defined, with no apparent interruptions from TDs. Figure 2b shows a magnified STEM image of a single quantum well, indicating presence of ultrathin layers sandwiching the MQWs.…”

“…Since the significant carrier migration to the localized recombination sites (∼4.55 eV) observed in this range (5–90 K) has no notable influence on the radiative efficiency (IQE = A ( T )/A­(5 K)) of the MQWs, as indicated in the inset of Figure a, it is proposed that the constant τ PL is due to a dynamic equilibrium between the rate of carriers (from shallow sites in the sub-QW) captured by the localized sites within the main MQW (at 4.55 eV) and carrier escape from the main sites of MQW to other lower energy states, as shown in Figure c. These lower-energy sites can be due to lateral inhomogeneities in the MQWs. , …”

Reducing dislocations of thick AlGaN epilayer by combining low-temperature AlN nucleation layer on c-plane sapphire substrates

“…The intensity of AlGaN (0 0 2) for sample B is much stronger than that of sample A. Previously, it has been demonstrated that the X-ray rocking curve for the symmetric (0 0 2)-reflecting plane is related to screw and mixed dislocations, whereas the X-ray rocking curve for the asymmetric (1 0 2)-reflecting plane is directly influenced by all threading dislocations, including edge dislocations [12][13][14]. We believe that the improved crystal quality is related to the alleviation of lattice mismatch between AlGaN and the underneath sapphire substrate.…”

Investigation on HT-AlN Nucleation Layers and AlGaN Epifilms Inserting LT-AlN Nucleation Layer on C-Plane Sapphire Substrate

“…It was well known that the red-shift of AlN E 2 (high) phonon mode corresponds to tensile strain in the HT-AlN nucleation layer, which is caused by differences in the thermal expansion coefficient and lattice mismatch between the AlN epilayer and sapphire substrate [5,9]. The theoretical value of E 2 (high) for AlN is 657.4cm -1 of stress-free [13,14], so there existed red-shift of AlN E 2 (high) mode of 6.4 cm…”