Metalorganic chemical vapor phase deposition of thick, crack-free GaN on Si can be performed either by patterning of the substrate and Selective growth or by low-temperature (LT) AlN interlayers enabling very thick GaN layers. A reduction in dislocation density from 10 to 10(9) cm(-2), is observed for LT-AlN interlayers which can be further improved using monolayer thick, SixNy in situ masking and subsequent lateral overgrowth. Crack-free AlGaN/GaN transistor structures show high room temperature mobilities of 1590 cm(2) Vs at 6.7 (.) 10(12) cm(2) sheet carrier concentration. Thick crack-free light emitters have a maximum output power of 0,42 mW at 498 11111 and 20 mA. (C) 2002 Elsevier Science B.V. All rights reserved.