Role of Hydrogen in the CVD of Wide Bandgap Nitride Semiconductors

Abstract

Hydrogen is an important component of the gas‐phase growth chemistry for GaN, which is typically based on NH3 and (CH3)3Ga, and also the processing environment for subsequent device fabrication (e.g., SiH4 for dielectric deposition, NH3 or H2 annealing ambients), and is found to readily permeate heteroepitaxial material at temperatures ≤200 °C. Its main effect has been the passivation of Mg acceptors in p‐GaN through the formation of neutral Mg‐H complexes, which can be dissociated through minority‐carrier (electron) injection or simple thermal annealing. Atomic hydrogen is also found to passivate a variety of other species in GaN, as detected by a change in the electrical or optical properties of the material. The injection of hydrogen during a large variety of device fabrication steps has been detected by secondary ion mass sprectrometry (SIMS) profiling using 2H isotopic labeling. Basically all of the acceptor species in GaN, i.e., Mg, C, Ca, and Cd, are found to form complexes with hydrogen.

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…a recent review in Ref. [32] and references therein, we will be discussing these matters later in the paper). Theoretical studies of hydrogen electronic states in GaN have been performed in a number of papers [33][34][35][36][37][38], a very good summary of the results can be found in Ref.…”

“…Only at even higher temperatures is the conductivity determined by the holes activation from the impurity band into the valence band. The activation energy of this process, e 1 , is the sum of the depth of the Mg acceptor level E a (Mg) and the e 3 activation energy [32]. A comprehensive analysis of the temperature dependences of the hole conductivity in p-AlGaN:Mg has not been systematically done as yet.…”

Electrochemical potentiostatic activation for improvement of internal quantum efficiency of 385-nm ultraviolet light-emitting diodes

“…In this work, we confirmed that the EPA process reduced the hydrogen concentration by 35%, thus increasing EQE and IQE by ∼20%. Although hydrogen is removed from the Mg H complex, only ∼10% of the Mg atoms are ionized to generate hole carriers, because the ionization energy is too high; E a = ∼170 meV [21]. This means that a small increase in hole concentration can effectively improve the performance of GaN-based optoelectronic devices.…”

“…A large area of the peripheral region of the LED epi-wafer was not exposed to the HCl solution for the EPA, but displayed the same hydrogen SIMS profile as the solution contacted area. It seems that hydrogen diffusivity is high enough that Mg H bonds could be broken almost evenly by the electric voltage all around the wafer, regardless of the contact to the electrolyte [21]. It is assumed that hydrogen would take the form of a positive charge (proton) after the Mg H bond breaking, because a positive current is applied to the LED epi-wafer.…”

Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

“…This concept has been utilized to improve transistor properties in silicon devices through hydrogen passivation or forming gas annealing in order to passivate the dangling bonds at the Si/SiO 2 interface. [8][9][10] Hydrogen in an Mg-doped GaN epi-layer has been a technologically critical issue in the growth of p-type GaN.…”