Investigations of GaN surface quantum well in AlGaN∕GaN transistor heterostructures by contactless electroreflectance spectroscopy

Abstract

Al Ga N ∕ Ga N transistor heterostructures, caped by ∼2nm GaN layer, were investigated by contactless electroreflectance (CER) spectroscopy at room temperature. Below the AlGaN-related transition CER spectra have shown a clear resonance at the energy of ∼3.7eV, i.e., at much higher energy than the GaN band gap energy. The observed feature has been connected with the optical transition within the GaN cap layer. It was concluded that a surface GaN quantum well has been created by the deposition of nominally undoped (or Si-doped) GaN cap layer on AlGaN∕GaN transistor heterostructures.

Luminescence and reflectivity characterization of AlGaN/GaN high electron mobility transistors

“…τ NR -1 ≥ (S+S')/d, point to negligible surface recombination. We finally mention that the cap luminescence studied in this work is at lower energy than previous reports on (Al,Ga)N/GaN HEMTs cap emission [17,18], and it is not clear whether this is simply due to differences in injection intensity.…”

Above GaSb barrier in type II quantum well structures for mid-infrared emission detected by Fourier-transformed modulated reflectivity

“…One could imagine an existence of a kind of surface QW formed of the GaSb cap and confined by the vacuum potential on one side and AlSb layer on the other (partly, as this is only 2−nm thick). Optical transitions related to that sort of surface QWs have already been reported in different material systems, also by using modulation spectroscopy in GaAs [9], GaN [10], SiGe [11] or ZnO [12] systems. For the purpose of the current discus− sion, there have been investigated three W−shape QW struc− tures differing only in the thickness of the GaSb cap layer, i.e., the layer terminating the entire sample (all the remain− ing GaSb layers and InAs layers are identical in these three samples and equal to 25 and 2 nm, respectively).…”

GaN Surface Quantum Well In AlGaN∕GaN Transistor Heterostructure Studied By Contactless Electroreflectance

“…The transistor heterostructure is very similar to samples, which are discussed in Ref. [1], and is composed of 2-µm-thick GaN buffer, 20-nm-thick AlGaN and 2-nm-thick GaN cap layer. In order to measure CER spectra, a standard experimental set-up with homemade semitransparent capacitor has been used [3].…”

“…It is expected that the energy gap of GaN cap layer should be higher than the bulk GaN energy gap because of the quantum confinement effect, which is strongly manifested at such a small thickness of semiconductor layers. Recently, a clear experimental evidences for this effect has been provided by contactless electroreflectance (CER) spectroscopy [1], i.e., an absorption-like technique which is insensitive to optical transitions associated with defect-states [2][3][4]. It is worth noting, that the deepness of sample probing by CER spectroscopy is strongly limited for AlGaN/GaN transistor structures due to the screening of elecromodulation by the sheet of two dimensional electron gas (2DEG) at the AlGaN/GaN interface [5,6].…”