This paper addresses the role of generative AI (GenAI) for autonomous optimization of next-generation wireless networks and the generation of xApps and rApps using large-scale language models (LLMs) within the Open RAN (ORAN) architecture. To address the high cost and resource consumption of conventional LLM fine-tuning, this paper proposes a Retrieval-Augmented Generation (RAG)-based approach. Specifically, we compare and evaluate three approaches: vector-based RAG, GraphRAG, and Hybrid GraphRAG, using the ORAN specification, and analyze their performance in terms of fidelity, answer relevance, contextual relevance, and factual accuracy depending on question complexity. The results show that GraphRAG and Hybrid GraphRAG outperform conventional vector-based RAG, and in particular, Hybrid GraphRAG improves factual accuracy by 8% and GraphRAG improves contextual relevance by 11%.