[ME05] Wet etching of GgAs for lateral PIN photodiode

Introduction Photodiode play important roles in optical communication systems nowadays. In this field, fiber optic cable is used as an information signal transmission medium between the light sources, sensors and photodiode. Many materials can provided to make the photodiode substrate in order to produce the detector to be used in application that require higher bandwidth and long distance transmission. Therefore, the optical receiver for long-distance telecommunication has primarily been implemented in III-V materials like GaAs or InGaAs in order to achieve the highest possible performance. InGaAs/InP PIN photodiodes are highy promising devices for usage in high-speed photodetector system in optical communications because of their excellent frequency and low-noise performance. This high performance is due to the high mobility, high saturation velocity and high sheet-carrier density of the InGaAs/InP system. The fabrication of InGaAs/InP photodiode necessitates pattern transfer techniques with a high degree of precision and a variable anisotropy [1]. Since the recess formation for the schottky gate is the most critical procedure in the fabrication of photodiode, the selective etching of InGaAs on InP is a useful technique for obtaining high uniformity. Wet chemical etching is a simple technique that offers high selectivity and prevents deep damage to Quantum Well (QW) layers when compared with dry etching techniques [2]. Selective wet etching has three main advantages over dry etching like it causes no damage, it is less costly and it is more reproducible. Besides that, three main purposes are to form pattern to polish and to enable visualization of defects or damages [3]. Wet chemical etching has been the technique most widely employed in device fabrication. Wet chemical process include pattern formation, polishing and detect or damaging visualization [4]. Selective wet etching using a solution of phosphoric acid and hydrogen peroxide is widely used for gate-recess and mesa-sidewall etching due to its relatively high selectivity. Most etchants for III-IV compound materials such as InGaAs and GaAs contain an oxidating agent, a complexing agent and a dilutant such as water. The oxidizers usually are Br2 [5], H2O [6, 7, 8], AgNO3/CrO3 [9], HNO3 [10] and NaOCl [11]. The oxidized layer is usually insoluble in water. It is made soluble by complex agent such as NH4OH [12, 13, 14], NaOH [15], H2SO4 [16, 17, 8, 15], HCl [8], HF [9, 18], H3PO4 [19] and critic acid [6]. This paper described how permanent alignment marks for the GaAs Lateral PIN photodiode are created using GaAs wet chemical etching technique. The substrate-tophotomask alignment is vital in the fabrication of the GaAs Lateral PIN photodiode as several processes required that the dielectric layer to be removed. The removal of this dielectric layer prevents any alignment to be made between the present and subsequent layer, as any marks created on this layer will be completely eliminated.