Porous nitride semiconductors reviewed

Abstract

Porous nitride semiconductors are a fast-developing area of study, which open up a wide range of new properties and applications, including strain free optical reflectors, chemical sensors and as a pathway to device lift-off. This article reviews the current progress in porous nitrides formed through electrochemical and photoelectrochemical methods. Using a simple electrochemical cell, pores are formed by injecting holes into the surface layer in order to oxidise the material into a soluble form and releasing nitrogen gas. The process is controlled principally by the electric field that drives the injection of holes and hence the applied potential and doping density are the key parameters for controlling pore morphology, along with how and whether illumination is used. We describe the mechanisms responsible for this process in detail and outline the trends for changing pore size and pore shape. For example, larger applied potential creates a larger electric field and hence larger pores. These methods have been used to produce a wide variety of different structures. We present a layered porous structure created by the modulation of the applied potential. Alternatively, layered structures can be produced by growing alternate doped and non-intentionally doped layers. Electrochemical etching can then create pores only in the doped layers, as they are conductive. This process can be performed by etching laterally through access trenches that expose the doped material or through the etching of dislocations to create nanopipes that allow subsurface porosity to form. This process requires no prior processing steps. We combine this method with patterning of surface protective layers to influence where the resulting pores grow. Based on these various fabrication processes, significant progress has been made towards applications of porous GaN across optoelectronics, sensing and for improving material quality.

Patterned III‐Nitrides on Porous GaN: Extending Elastic Relaxation from the Nano‐ to the Micrometer Scale

“…GaN or InGaN, was porosified via electrochemical etching in oxalic acid from the side of an etched mesa or ridge, following the previously reported process for porous‐GaN‐based mirrors, one of the main applications of porous GaN to date, taking advantage of the differences in the refractive indices between solid and porous GaN. [ 20,43 ]…”

Early Attainments of Porous Silicon Carbide Technology: a Bibliographic Digest

“…Detailed study of the properties of such films was done in [51] According to the Auger electron spectroscopy data, 5+0.5 at.% average deviation from the starting material stoichiometry towards elemental carbon enrichment was determined within the anodic films formed in HF-based electrolytes with ethanol in several concentrations. In addition, an elemental analysis performed with electron diffraction spectroscopy showed that the films were enriched with oxygen and fluorine at the level of (5-7) at.% and (7)(8)(9)(10)(11) at.%, respectively. It was found that the samples with an increased content of detectable chemical impurities had pronounced photosensitivity.…”

“…Here we note that Lee Canham subsequently pioneered the biomedical applications of porous silicon as well [4]. To date, there have been several generalizing reviews on the recent results of obtaining porous structures based on semiconductor materials and compounds and the prospects for their application for modern micro-and nanoelectronics, sensing and biotechnologies [5][6][7][8][9][10][11].…”

Porous Nitride Light-Emitting Diodes

“…Porosification of semiconductors as a way to control their optical and electrical properties has been studied in different materials since many years. , In nitrides, additional interest in porosification stems from the strain and dislocation density reduction when using porosified buffer layers. − This property is particularly important for nitride growth on Si substrates, for which the mismatch of thermal expansion coefficients and the dislocation issues are severe.…”

“…To solve this issue, porosification was proposed as an attractive alternative to accommodate the strain. Nitride layers can be porosified using wet etching with HF or KOH, reactive ion etching or electrochemical etching (ECE), and photoelectrochemical etching (PECE) . LEDs grown on porous nitride buffer layers were reported showing improvement of their performance. ,, …”