Ultrasmooth V‐Grooves in InP by Two‐Step Wet Chemical Etching

Abstract

A two-step wet chemical etching process using HBr and HBr:K2Cr2O7 was developed in order to fabricate high-quality V-grooves in InP (100) wafers. A 40 nm titanium film, which was patterned by conventional photolithography and liftoff, was used as the etching mask. The {111}A sidewalls are mirrorlike with an arithmetic average roughness of less than 0.4 nm. The tip radius of the V-grooves is approximately 7 nm. Both values were determined by atomic force microscopy. InfrocluctionEver since they were first suggested, low-dimensional structures have generated wide interest. Due to their reduced dimensionality, the electronic density of states is increasingly confined from the common square-root dependence in bulk semiconductors through a steplike function for two-dimensional quantum wells (QWs) and sawtooth-like singularities for one-dimensional quantum wires (QWRs) to S functions for zero-dimensional quantum dots (QD5).' From the device point of view, the steady constriction of the density of states has several beneficial results, since basically the distribution of electrons and holes over a wide energy range is eliminated, thus leading to improved device characteristics. For lasers with quantum structures as the active region, the threshold current density becomes smaller' and less temperature-sensitive2 with decreasing dimensionality. Simultaneously, the optical gain increases dramatically.' Due to the modified density of states, the linewidth-enhancement factor is expected to be extremely small,3 which leads to improved noise behav-ior3'4 and increased relaxation oscillation frequency.3A QW laser can be easily grown on planar substrates by controlling the growth time. The main impediment of realizing QWR and QD lasers is the very size of the quantum structures in two or three dimensions lying in the range of de Broglie's wavelength.GaAs/AlGaAs QWR lasers have been fabricated using anisotropic growth in V-grooves.5 Conventional lithography in combination with wet chemical etching was used to fabricate the V-grooves. The lateral current confinement was realized by H-implanted areas which must be aligned with a precision of less than 1 p.m. Such accurate alignment is unnecessary if a set of QWRs is used in parallel.6 Lasers with strained self-organized QD5 grown in the Stranski-Krastanov mode were demonstrated.7 The

Filling transition for a wedge

“…However, e.g., in the context of structured semiconductor surfaces [17][18][19], microfluidics [20][21][22][23][24], and templates for the selfassembly of small particles [25][26][27] highly regular nonflat lateral surface structures can be produced. But both the theoretical understanding of the local wetting phenomena in such structures [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] as well as corresponding experimental investigations [43,44] are still in their infancies [45].…”

Phase behaviour of fluids confined between chemically decorated substrates

“…The emergence of a number of novel techniques in materials science, such as lithography [1,2], wet chemical etching [3], and microcontact printing [4][5][6], has permitted the fabrication of solid substrates with stable, precisely characterized surface structures on length scales ranging from microns to nanometres. Such chemically decorated substrates play an important rôle in a 1 Guest scientist of Sonderforschungsbereich 448 'Mesoskopisch strukturierte Verbundsysteme'; permanent address: Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln NE 68583-0915, USA.…”

Wet-etch bulk micromachining of (100) InP substrates

“…In their fabrication anisotropic wet-etching of InP is used to form specific device features, including ridge-groove patterns for diffraction gratings [3,4], V-groove patterns for quantum wire structures [5,6], and alignment grooves for monolithic integration [7,8]. It is also applied to release suspended semiconductor membranes [9,10], and to form emitter-or collector-size-reduced self-aligned hetero-junction bipolar transistors [11,12].…”